Wow - that's a lot of assumption on your part. From knowing a few of the guys that are bidding from one Class 1 airframe to another Class 1 plane, some of them simply prefer the sort of flying the non-APU fleet does. Not everyone is chasing type ratings or trying to "hide out" in training.
As for going to one payscale, that's a rumor with IBB: at least, combining Classes 1-3 into a single grouping is the rumor I've heard. But that still won't stop some of those darn captains from switching fleets. Some people just want an APU and/or have the ability to fly a little more outside of the conntinental USA.
Be careful painting people with a broad brush. There are a lot of reasons why people make the fleet choices that they do and that is a seniority right in our contract.
And trust me, I'm trying to move out of my current fleet so hopefully someone can upgrade in the near future.