So interestingly, I looked at the very first E175 bid packet and I noticed there are only 16 active pilots bidding for lines, plus 4 management pilots. There's a huge number listed as ULA, including the top-of-the-list ASA pilots. So it seems like a lot have left or retired.

Maybe they're not yet qualified? But then they probably wouldn't be listed as ULA, they'd be paid off-line.