[jrauser]

Your control is greatly reduced in aerobars, but more importantly, your ability to defend your space is hugely reduced, which makes riding in a pack extremely dangerous. This video explains why having the ability to protect your bars prevents crashes: https://www.youtube.com/watch?v=sRIsWzrMmBs

Cycling has some dumb rules (e.g. sock length), but banning aerobars in mass start races is not among them.

[ufmace]

This. Aero bars are nice for flats and descents. I wouldn't want to have to do a tough climb without drop bars or at least flat bars. And I definitely wouldn't want to ride in a pack with drop bars with my hands not on them. That sounds like a great way to wreck.