It mostly seems like your personal experiences and server choices might be giving you the wrong idea. It might be the reason your communities don't make the switch, but the wider userbase doesn't really know about any this at all.

If it was as prevalent and the big reason, plurality would be more common in general servers or those dedicated to some other topic. It's my, and probably a sizeable portion of people's, first time hearing about PluralKit. Even knowing about plurality and systems prior to this. I'm in a bunch of servers with indescribable amounts of people and this really hasn't come up at all.

If you were to ask a random discord user/mod/server owner why they don't switch to Matrix, they most likely won't answer "It doesn't have PluralKit and I/my friends use it", but "What's Matrix?/What's PluralKit?/How so you use it?/Discord's fine/But why?/IDC"

Like, all power to you, this shows an important missing feature for your community in Matrix, but I don't think this is it.