I try to do at least my roulette every day on my paladin, but I have to agree with some of the sentiments I have seen out here so far: It's kinda nerve wracking at times. Folks get *really* up tight even in non-end game dungeons and I can't fathom why.
For the most part, I have great runs with a lot of friendly and understanding folks. However, it only takes a few bad instances to make me want to only tank for my FC. Last night I had my second *bad* run. I had a sch healer who was spending more time DPS'ing than they were healing (clearly trying to speed the run up, nothing unusual about that), this wasn't a big deal, but I got killed as a result of it. Again, no big deal but I died before a boss room (First boss of Sunken). They rezed me, so I had the death penalty on me. I remembered that this boss can actually hit pretty hard at times, and where I had nothing to negate crits and the like due to synch, I wanted to wait to get rid of the penalty. You know, all of two minutes. That's when the insults and put downs started.
Now, this part was on me I think, but between the sch and the black mage in the party, I was having a bit of trouble holding the aggro on everything. I was managing, but some stuff would slip away which I would then switch focus to in an attempt to pick it up. This became somewhat of a topic to needle at me while I waited for the penalty to wear off, but I decided to just brush it off and not say anything back. Try and learn from it, etc. After the first boss went down I continued on, only to notice that the heals were only coming in when I was near death and that no one was following my marks at all. In fact, they were reassigning the marks on their own. Everyone was just attacking whatever they wanted and honestly, I just about lost my patience. Regardless, we cleared the dungeon but I couldn't help but notice that at the end one of them put "Fail tank" in the party chat as I was leaving the dungeon.
It was nearly enough to make me not want to tank a dungeon again.
TL;DR version: A few rotten apples make people not want to tank/heal. It's not the sole cause of the shortage, but something that can really go a long way in making people want to tank is to try and be friendly and understanding with folks, regardless of job or role in the party.