I suspect the crew you saw walking were Jet2 crew. They have a very “robust” disciplinary process for late crew members and most are on temporary contracts. You can understand why the crew choose to walk but it’s not something I want to do before a long duty.
If it were Jet2 crew then they shouldn't have been feeling they needed to walk, Jet2 crews have all been told explicitly that if the car parking and bus causes them to be delayed then they will not be investigated for being late.