Don,
It can happen for many different reasons, but it’s, I dare say never, but very often not ATP’s fault. I had to buy extra time during the Instrument phase. My study habits were lacking. I put too much faith in my instructor and not enough in myself. I should have taken initiative on day one. Because I didn’t, I ended up having to purchase additional flight time. It was my knowledge that needed polishing, but I had to stay proficient in the plane.
I learned a valuable lesson from that experience. It inspired me to write about it.
https://airlinepilot.life/t/what-does-an-atp-student-need-to-do-to-be-successful/10421/5
Tory