Is it trend for senior group fans to hate on junior groups?

sure why not

Boomers hating genz nothing new

Thats a given... it escalates when the older group is not being promoted well and the junior one is getting all the support lol. Too many examples to give sadly

It's not a trend because It has always been there, but It isn't something that can be helped: even New Jeans stans will become bitter at younger stans when the 6th generation will be a thing.

I wouldn't say It's only based on the envy fans get seeing that their favourite idol group is not on top of the world anymore, It's also because as a fan, you start to feel first hand how the Kpop industry is disposable, because nowhere in the world 30-year-olds are considered senior citizens, but for Kpop idols (especially the women) it is kinda like that, and as a fan of 30 year-old idols, you feel the unfairness of this machine. So you eventually get mad at the newer fans who call your idols 'old' and some people may start to exibit some toxic behaviours.

this mainly happens if the fans of the senior group see the juniors as a threat/replacing the older group. Tge most obvious example of this was Blackjacks hating Blackpink, but it kind of happened with CLC and 4Minute too.

Yes, kpop fans hate when new groups debut and dare show their faces quite a bit as they see them as a threat.

It's always there in kpop. The company turns its attention, $$ and emphasis towards the new group, which makes fans of the older group resentful. The older group gets cheaper MVs and shorter promotions while the new group seemingly gets the world. There's also a feeling that the older group is carrying the newer group with its dollars as that group gets up to speed. (Of course no one considers that once the newer group is up to speed, it will help carry the older group, which usually isn't making as much money as it used to, because of enlistments or shifting consumers or aging fandoms, but whatever.) Adding salt to the wound is the way the newer group is often paired with the older one, which again makes them feel like they're riding on their coattails.

This isn't actually too different from other business models, to be fair. What's new needs constant promotion to build interest, trial and awareness. Less dollars are spent on established brands with a loyal fanbase because those fans will show up.

(What's wilder still to me is watching this happen in NCT, a group that's meant to expand limitlessly. I see people complaining that newer members are riding on the coattails, like what , do you even understand the group's freaking concept?)