Why has nobody been using them more?
Simply put, it's our choice.
When I make a team I usually don't think about typing yet, I think about a lead. I build a team around that lead. If a Fire Type is not needed then, I won't put in on my team, especially if I have a Flying Type that covers grass, a Ground to cover Steel, and a Fighting to cover Ice. It just varies; and I may not even need the coverage I listed.
Some of those mons, and others, deserve a tier bump! Why has nobody been using them more?
Again it varies on it neediness on a team. I understand the Gale Wings Talonflame is very strong in certain cases, I acknowledge that, but I'm not going to randomly throw him on my team just because it got popular. Besides it's usage that give them a tier bump.
Fire got a new resist, fairy, and nobody talks about! Why not?
Umm, it's just a type resist. Steel types are resistant to them as well, so..
Am I the only one who noticed the buffs to fire types this gen???
No, everyone has to acknowledge the facts, it's just up to us to either utilize it or plan against it.
Since this question relies heavily on opinion (IMO), I'll hide if not accurate enough.
Hopefully I've Helped!