It’s simple, I will explain. The twin engine design of the P-38 didn’t allow for effective cockpit heating given they’re on external booms. The heated suits were notorious for failing, hence P-38 pilots froze their ass off. Honestly after all of the problems with it were solved it was a good plane, just not a great plane. ETO had two great planes hence there was no need for the P-38.
Then so did bomber crews but I haven't heard much about that over the years.