I’m not going to claim to speak for all tanks. I will provide a list of reasons why there is a perceived shortage of tanks. Heroics aren’t hard, but they do have a gear limit which is honestly a low floor, but it does need to be met as a tank/healer.
It’s not as much raid composition though this contibutes.
It’s the PUGs.
I cast faerie fire. You cast CL/Arcane Explosion/Multi Shot you name it. Mobs run everywhere. Healer pulls aggro. I have 0 rage because you didn’t let them hit me.
Priests pre-shielding me drives me nuts. I get no rage at the start of the pull which is the time I’m putting in the most work to establish threat.
Reacting to a botched pull/body aggro by absolutely going berserk with dps instead of, say, CCing something, or off healing.
Complaining about having salvation and not kings/might/wisdom then pulling aggro.
Wanting to do YouTube FOTM hyper skips that other people aren’t familiar with, and you end up wiping. How much time did we save not pulling that first pack in SP then you aggro’d a Champion which feared us into the slave handlers?
Not having enchanted/gemmed gear(even budget enchants) and trying to do heroics in questing greens. As a community we’re not really geared to carry 2 people in a 5 man yet.
DPS not knowing to shock a caster that won’t los because someone dropped aoe on it before the tank touched it and now it’s free casting.
DPS not knowing how to LoS.
“xxx is res, LFM Tank” Yep, see ya.
Had a DPS running around instantly herbing everything and not sharing, couldn’t kick him because surprise the group leader was his guildie, didn’t wanna leave because was in a group where my BiS drops.
I have global cooldowns and I’m competing against 4 global cooldowns.
This is just off the top of my head, I’m sure other tanks can chime in as to why and if they even tank for PuGs.