I guess we could also say that by the 1950's the new crop of younger writers, directors, producers, etc, were infiltrating the new Hollywood machine, with grand schemes of new territories to unleash.
It makes a lota sense that with what, the bomb, the commies, the other side of the sky.......... The new radioactive paranoia was an unlimited treasure trow for the studios.
Put thy old guard out to pasture. Though they probably still had talent and ideas to contribute.

"You can't smell any reefer, can you"?