It's hollywood history... not your grandfathers
Remember, in hollywood ice sinks

Staying with bombers is very bad:
1. bombers are sloooow, fighters would burn a lot of fuel flying well bellow their cruise speed;
2. bombers are always attacked by fighters having energy advantage (speed and height), as escort you also want to have higher energy to engage other fighters;
3. .50 cal are unhealthy, and we are talking hundreds of planes, each having 10+ machine guns spraying rounds EVERYWHERE with poor accuracy, chasing someone through engaged formation of bombers is just asking to be hit by stray bullet.