You're forgetting an important thing- 9/11.. and maybe a few others. The massive bankruptcy rape that 9/11 brought down on the 121 world seriously bottlenecked lifetime earning potential. The whole reason people ran like rabid lemmings to the regionals in the 90s was promise of fast upgrade, high turnover, and movement up to the majors and the big bucks. Then in the late 90s RJs hit the scene, and the rung in the ladder became a plateau.
9/11 killed the real big bucks in the sky in any rapid fashion. Since then things like the 3407 crash made the economic reality of airline pilots very obvious. I was phone interviewed for Michael Moore's movie segment on how far pilots had fallen economically. Pilots were his canary in the coal mine...
Since financial entities like Sallie Mae got wicked burned by loaning money to aspiring RJ drivers, they don't do it anymore.
There might still be some willing to show up for the gig as-is, but not nearly as many.
If projected airline turnover is as expected at all levels, we'll see an overall loss in the size of the so-called regional airlines.