Rockabilly has turned into a lifestyle brand and died out of relevance because it doesn't want its participants to be a mess.
The reasons people complain about things are usually the same reasons they like those things. One of the defining characteristics of any scene or subculture is a bunch of people within that scene complaining that it's just a bunch of poseurs. If this complaint isn't made about a subculture, the subculture probably doesn't exist at all.
Subcultures are driven by a universal human need for acceptance; that's also how they end up full of poseurs. We want to package ourselves. We want to be capable of being known. We want to be welcomed. We find that we can often guarantee a welcome by imitating the structures of a pre-existing community. A subculture is a dance diagram for being loved: follow these simple steps and here's a home.
Rockabilly is a musical hybrid of two things that already heavily influence each other. In some ways its two parents seem too incestuously close to allow offspring. A mashup of rock 'n' roll, and country music ("hillbilly music"), it's a revival scene already on its second or third revival. Country and blues music began combining with some form of rock 'n' roll as early as the 1930s. Elvis is of course the reference point here, spanning country and rock 'n' roll, and defining rockabilly to the cultural imagination.
In the '90s and early '00s, rockabilly enjoyed yet another revival. It nostalgically styled the American 1950s in all their high-maintenance greaser kitsch: Girls in bullet bras and bright red lipstick, boys with greasy hair and tight jeans, cigarettes rolled in their sleeves. It also spawned a lot of bands, Social Distortion probably being the best-known representative, who enjoyed legitimate musical success. For a while tattoos and greaser hair and classic cars all pointed toward a particular fusion of country and blues with raucous, danceable, old-fashioned rock 'n' roll.
But today few, if any, of those artists are known outside of rockabilly scenes, and few rockabilly scenes still exist outside of very specific locales. Many other subcultures seem to have come back around quite recently -- goth and rave scenes enjoy their own revivals currently, and punk is always enjoying a revival, in that it never exactly dies. But rockabilly doesn't seem to have come back around with them.
Musical cultures known more for fashion than for music become at best jokes and warnings. More frequently, they just fade away. Rockabilly became popular again during a larger craze for midcentury Americana, the wider cultural trend that found every bar in Brooklyn hosting a retro burlesque show. Rockabilly become part of our brief obsession with the era when our parents were young (our mothers, perhaps, screamed about Elvis. We screamed about other people's memories of screaming about Elvis). But since then, this trend has for the most part disappeared.
Viva Las Vegas, a yearly rockabilly convention in Las Vegas, is one of the biggest rockabilly events in the world, if not actually the biggest. I read two-thirds of the event's homepage before realizing they hadn't yet mentioned a band or a music stage. Viva Las Vegas comprises a car show, a burlesque competition, a pool party, a swimsuit competition, a vintage fashion show, a (presumably vintage-flavored) bowling event, and the Guitar Geek Festival Show, which does in fact involve musical performances but is primarily a showcase for "cool vintage and weird guitars." Rockabilly, it seems, still exists in Vegas, but the objects are the point, not the music.
In fact, rockabilly's biggest scenes are currently located outside of America, in Japan and in Germany. In Japan, rockabilly culture exists under the canopy of the Harajuku fashion subculture. Rockabilly boys congregate in Yoyogi Park, their greasy pompadours gleaming, their leather jackets styled to a terrifying level of specificity. To generalize wildly, it makes sense that this American subculture enjoys consistent popularity in a city where aesthetic is king. Rockabilly boys are categorized alongside Gothic Lolita girls, a subculture that begins and ends with fashion. For the most part, the music in the Tokyo scene seems to be recorded, not live. Rockabilly boys and girls dance primarily to old records from the 1950s and 60s. Here rockabilly divorces itself entirely from a living music scene, and exists as a pure aesthetic.
The scene in Germany skews more toward psychobilly, the marriage of rockabilly and punk. This hybridization is likely due to Germany's strong pre-existing punk scene. Still, even there, what defines rockabilly and psychobilly most seems to be the aesthetic, performative and semi-ironic American fashion. The fact that rockabilly, a definitively American subculture, thrives outside America may explain why it hasn't come back around in its own country.
Camp and kitsch need distance in order to be successful. It's not surprising that a subculture so aggressively based on Americana is more popular outside of America. In Germany or Japan, it's easy to turn Americana into a fantasy and a form of cos-play (also super-popular in Japan). Americana in America, however, immediately refers back to a very present reality. It's difficult to maintain a fantasy when that fantasy is based on nearby realities of rural America, on the still-living grit and history of country music and of country itself.
The fad for our own midcentury, our strange nostalgia for our parents' youth, also seems to have lost popularity. Vintage 1950s and '60s styles were everywhere a few years ago; Mad Men was more a catalog of urban lifestyle porn than a television show. But this lifestyle seems to have lost its appeal, and perhaps that's because it reaches back to an era of greater repression. Other subcultures are about anarchy, messiness, and the loss of control. Music thrives on rebellion, whether literal political anarchy in the case of punk, or the defiant loss of control signified by scenes with heavy drug cultures (a factor in rockabilly's loss of popularity may also be that it seems never to have had much of a drug culture to speak of.)
The thing is, people don't want to get their shit together. People don't want to get up in the morning, and wash their face, and do their hair, and match their shoes to their clothes. In the end fewer people stay loyal to things that ask for cleanliness or good manners. Punk can't die because punk is about not giving a fuck, about not getting up in the morning, not doing your hair, not washing your face, not remembering your manners and not pretending you aren't blindingly angry at just about everyone you've ever met. A similar point could be made about the rave scene, with its vast enabling of incredibly stupid outfits and myriad drugs. We turn to music, the kind of music that grows a scene around it, because we want to escape from the strictures of good manners, not because we want to obey them. We go to music and its scenes because they let us be a mess. Because they require us to be a mess.
Rockabilly has turned into a lifestyle brand and died out of relevance because it doesn't want its participants to be a mess. Rock 'n' roll has always been a music of anarchy and rebellion. Country music, hillbilly music, deep blues out in the untamed big hills, is lawless, descending into the wide and bitter narratives of loss and lack. But the 1950s, the era from which the subculture gets its fashion, is governance and repression. The 1950s are your dad, and rock 'n' roll is about rebelling from your dad. The fashion and the music are contradictory; one subsumes the other. Repression makes for some sexy outfits, but it eventually devours itself, an equation that gives an endlessly smaller result.