Tanks can't keep aggro.

[technole]

At equal level, if a Tank is losing aggro then either they suck at Tanking, or the Healer / Dps are being asshats. Pld's have the lowest enmity multiplier by far (Cuz' SE is stubborn and refuses to fix anything that is wrong with that job, for some reason), and even they can hold enmity if they use their rotation correctly. Drk's and War's shouldn't have any problems at all establishing and keeping enmity.

...

It's also noteworthy that a lot of the DF tanks people run into are not actually Tanks. They're Dps/Healers who got fed up with long que times and swapped to get their Roulette's done. No surprise that they don't know the job well when it's not their main.

Regen pre-pull isn't going to cause anything more than an annoyance as it doesn't require a provoke to gain that hate. Tanks can simply click it off if they notice a mistimed one. It's not always the healer's fault for those (last mob dies before it's full effects, or tank hesitates on pull). A simple lob/scorns is going to take it back right away.

Some PLDs can't hold threat is because they usually are undergeared, full of VIT, and not hitting Halone combo and just whacking their Royal Authority. I know many get annoyed at having to use Halone. But if they wise up with stats, actually pull with Shield Lob instead of face pulling, and using Scorns on cooldown in AoE mobs they wouldn't have so much trouble.

Plus many of these tanks haven't leveled up solely on dungeons, you know where you actually get to play your job all-the-time. The amount of "oh I leveled on FATEs" tanks I hear in some places is almost sickening. Level 60 isn't the level to learn to tank.