Having flown for a second tier company for a while prior to being hired by United, the answer was clear to me. A lot (and I can't emphasize that enough) of the pilots who were rejected by the majors had checkered pasts. Those that didn't have checkered pasts eventually moved on to the majors. Sure, there were a few who stayed by choice. A very few.
As for your coworker who was sent out the door, it's clear that both you and he didn't know the ground rules for an interview at United (and every other major; it's just that United gets the bad rap for calling guys on this). The first hurdle was correct logbooks. You may not like it, but that's the way the game is played. I spent a week with my calculator and logbooks before every interview that I had. And logbooks are just the start of an interview prep.
A startup will always find qualified pilots. Quality pilots is another story.
Hmm...I was sure it was ...um...other things.