[PeterisP]

There are (and always has been) many groups - it's particular memes or styles/groupings of memes which tend to be specific to some particular subculture, not the term "meme". Perhaps decades ago the internet was narrow enough to be considered a single in-group, but IMHO that wasn't the case already for the first memes that the OP (and their particular ingroup) considered, i.e. in the mid-2000s. It's obvious that the memes of the older in-groups are not known by OP and their in-group, and in a similar manner OP is complaining that they're seeing memes for which they're obviously not the in-group anymore; and because of the regionality of memes IMHO it never was a shibboleth for just a single group; both the concept and the name was used worldwide in disconnected cultures speaking in different languages with each other instead of the english-centric majority of internet.

[skolskoly]

You might have misinterpreted me. I did not say there was ever singular in-group for the word, aside from the aggregate of all the groups that used it. The point is that the aggregate now includes everyone, and you can not have an in-joke that everyone is in on; that is just a regular joke. So, of course the appeal is lost to the people who enjoyed them for that fact.

But most people like regular jokes, and that's fine. As you suggest, "meme" began as an umbrella term, and various in-jokes will continue to be made, even without a word that specifically describes them.

The popularization of the term took about 20 years, and it looked a bit like an economic bubble: Many confused people, trying to mass produce things that are only valuable due to scarcity. Worse, it's a social phenomenon, rather than economic, so the process has been like watching a joke fly over someone's head a thousand times in slow motion.