If you look around when walk through a TfL station you’ll noticed that all the infrastructure is setup to make sure there’s more provisions for exiting a station, than entering the station. So the gates are setup to have more exit gates than entry gates, escalators set are always configured to have more up escalators than down escalators, routes through the station are more direct for exiting than entering etc.

TfL takes overcrowding extremely seriously, and have loads of provisions and strategies to prevent an overcrowding issue.

That's required because people tend to trickle into the station over time but flood when a train arrives.