There’s a psychological factor. Many people believed it wasn’t humanly possible to do a sub 4 minute mile before Bannister accomplished it.

Once that was done the flood gates opened and many others broke it in the following months. This is the “central governor” theory in endurance sports.

https://en.wikipedia.org/wiki/Central_governor

Nah, common misconception.

Progress had been steady for decades, but was interrupted by WW2.

There was one other person who did it a sub 4 minute a month and a half after him, then 3 more people the next year.

It was more down to improvement in training (Bannister was doing interval training, which was a new idea at the time).