Something something financial and temporal resources, honestly.
You can't easily shift motion-captured animation to different animation rigs and not have it get a little weird, after all. So can you imagine if every attack animation and all the movement animations and emotes were motion captured, and adding a new race that wasn't basically using another race's existing animation rig would mean you had to go do motion-capture for every single one of those? The amount of time and money involved would be dizzying.
And just taking, say, Roegadyn animations and going "we've got this 'hunched back' posture, we're going to just blend that in to every animation and call it a day" would work for some situations and not others. And considering how much fuss the playerbase has made over the lack of hats and hairs for Hrothgar PCs... can you imagine the fuss if like 80% of their animations looked "off" compared to the other races?
This is leaving aside the fact that, at least to my recollection, 1.x's animations caused some interesting situations in combat, because the engine seemed to prioritize animation fidelity over actually letting me put my character where I wanted to; I definitely remember watching it play a couple of steps after I stopped moving, letting the animation carry me into the edge of the AoE I was trying to stop short of. Because, y'know, can't just cut the animation short in a choppy fashion!
Don't get me wrong, I definitely miss the way 1.x characters felt like they had weight to them, compared to how we all seem to be a little floaty in the game nowadays. And the quality of the cutscenes was stunning in many areas. I'm just not going to look back at it through rose-colored glasses and pretend there weren't drawbacks to that scenario, too.