Why do people bother dodging aoe during trash pulls?

[Packetdancer]

We're strictly talking about trash pulls in dungeons here. Besides, in real raids failing to dodge an aoe results in a damage down which is bad for your numbers.

This is only my second savage raid tier, I'll grant, but my understanding is that in pretty much all previous tiers failing to execute a mechanic that didn't kill you usually resulted in a vulnerability stack; hence, a lot of people would just eat a stack in a survivable mechanic to maintain uptime if they figured the healer could still heal them through the next unavoidable raidwide even with the vuln.

So "just stand in the AoEs, the healer will adjust" is definitely a thing that people applied in real raids too, previously. (Witness, among other things, E6S soccer uptime.)

This tier's switch to having failure to execute a mechanic result in damage down instead—hitting people "where it hurts", as it were—is both a new development and, I suspect, the devs trying to eradicate that "just ignore mechanics/AoEs" behavior. Now ignoring a mechanic doesn't let you optimize your DPS output; instead, it has the reverse impact and instantly reduces the damage you're doing.