Bayh's problem is the feminist lobby hates his guts and will not stand for his nomination. Gore wanted him as his VP in 2000 and the feminists basically told him, "No." He listened.
He certainly isn't too conservative; that's not the issue here. The problem is what I stated above.
Why don't they like him? Is he anti-abortion?
If so - no thanks.
He's a centrist on abortion.
What does that mean? There are pretty much only the two positions.
He doesn't want it completely banned but he wants to ban partial-birth abortion and, I think, anything past the first trimester.