The point you are missing is there was plenty of room on the train as many other (able bodied) people got on.
Trains are never completely full, so yes if someone will not move to allow a disabled person to use the wheelchair space, then tough - choose between moving to somewhere less comfortable or standing on the platform and wait for the next train.
I have boarded plenty of trains that have been full to bursting, there are plenty in 2, 3 and even 4 car formations around this neck of the woods. And there are the some of the peak XCs which can be uncomfortably loaded with no room to move in any direction.