Mentoring - without being unkind to large GAAP, they seem to have a predominance of low time CPL working their way to the airlines by instructing. No criticism but their experience locker is still mainly theory.
I started at a GAAP in the 70's and had first hand experience of three instructors in three months.
Moved to a small 'ma and pa' school run by people who loved instructing and later over a brew or beer after would impart the wisdom gained by many years flying and instructing. First time I went outback they pumped me full of wise info that made it a great trip, first of many.
Might have saved my life a few times I reckon. They are still operating although have moved a distance away but I still fly there to do my BFR - because I'm still learning, and they are still mentoring.
And, yes, I know there exist some high time people at GAAP here and there - problem is tracking them down.