I think the weird ambiguity of some of these responses kind of summarizes the issue.
Subcultures just used to be way more blatant. The people who were in them tended to label themselves, and the people outside of them could easily identify them. The goths called themselves goth, and we all knew what the goth kids looked like. Same with punks and skaters and emo kids. The biggest exception was probably "preps" which was more of a label assigned by outsiders to generically trendy, upscale teenagers. And they were definitely subcultures as that single term encompassed how they dressed, the music they listened to, the entertainment they consumed, etc.
That notion of a solid, concise label seems to be what's missing. There's no shortage of distinct social groups and trends among them, yet there seems to be no real, encompassing label used by either side except stuff like "those kids who like A and are also usually into B and do C". Any label you can find tends to just define one aspect.