In search of good operating economics its engines were underpowered. I had many a scary take-off from Sumburgh airport flying in ATPs. It was very fuel-efficient, but slow. Also at the time the ATP was launched it was facing stiff competition from the newly launched Regional Jets, which airlines and passengers preferred. The Fokker 50, ATRs and DHC -8s all had the advantage over the ATP of good short-field performance.
Steve