Some FCs are more talkative that others, you might even find yourself a FC that talks too much lol. Or talks about stuff you don't want to read. Like you don't want your hunt LS to be massively chatty if you've got 3 of them, you just want them to announce hunts and be quiet otherwise .

I think you're facing potentially a combination of three issues.
  1. They could just not be as chatty as you'd like, they've got nothing against you or anyone else and they're not ghosting anyone as much as they just don't feel like talking in general. Which can be exaggerated quite a bit if you've got a lot of people who view the FC as social backdrop rather than a front and center feature. Like how some people don't want to bother putting together a party but enjoy the idea that they're in a live group, just silently doing things with other people- sort of a quiet social feeling (don't want to be alone, don't want to talk, let's just do this content together, my brain is unwinding right now).
  2. They're already doing something together and you're not part of the "in" "in" group yet. This can be hugely negative or mildly negative depending, on the treatment of others. From just real life friends who'd love to hang with others to that lovely super drama of the FC leader trying to court a GF and will burn everything down to make it happen lol. I see that happen more often for raid groups and stuff where you can't really share time as well (because rewards and learning are invested into that particular group).
  3. They've a discord and they're chatting there.

Personally I imagine #1 being a core part of it, with just a smidgen of the other two. Especially since you said they're nice. Usually it's pretty obvious if #2 is active, if it's the more active form then there is little hope lol. Of course there could be other factors, not pretending I've made the whole list but I find those likely and peaceful listing- like you could add #4 in which they don't want to play with a person because they're not fun / so awful at the game they required to be carried but that's not a very exciting concept to entertain lol.

So imo probably nothing against you, just not very chatty people silently bumping shoulders and existing in the world together as each other's "living" backdrops.

Can improve it by keep trying for a while and if you succeed you can change the fabric slightly and find particular people who are willing to step out of the living canvas, or finding a more active FC lol.