I would blame the content, rather than the community.
If the content weren't designed the way it is, the community wouldn't do what it does.

For one, content doesn't really teach people how to tank. So there are a lot of tanks who think that all they need to do is be the first guy to run in and hit stuff, enmity and cooldown management are unheard of. So no Flash/Overpower spam to keep aggro over AoE'ing DPS, and no mitigation to help healers keep them alive. Or tanks with extremely subpar weapons with a decent understanding of their skills, but no idea how much of an impact a weapon has on their ability to hold aggro.

For another, I think we've all heard that dungeons can be summed up as trash mobs -> boss -> trash mobs -> boss, etc. There's nothing interesting about the mobs preceding bosses, so they're trash, and people will want to steamroll/avoid them if they can be steamrolled/avoided. Like random encounters in typical JRPGs, they're just there to slow you down and don't require any skill to defeat. Even worse here considering they don't appreciably reward you for defeating them--we're not getting xp, they don't give much gil (if any), and there's no chance of getting useful, special drops.

Lastly, the game's mechanics are such that overly large mobs can be trivialized by gear, and especially by good skill usage. Almost every mob can be defeated within ~20 seconds, give or take a bit depending on party composition, and if everyone knows how to handle large pulls, it's not hard to do. But it's possible to advance with next-to-no-skill at all, at a much slower pace. The gap between what's possible to do and what the game teaches you you can do is tremendous, and many can't figure out how to cross that gap for their roles or jobs, or even care to. So you end up with a pretty clear division of Can- and Can't-Do's, so to speak.

I don't think it's fair to expect the community to behave any differently from how it does, or judge people poorly for what they do. The content is designed to allow such completely differing playstyles, and you can't choose your playmates in DF. Unless they implement filters for playstyle/purpose, sort of like how they do for PF.