A 4 sector night often does not provide you with sufficient time to hit the vending machines between flights, particularly if delays are incurred and your professionalism dictates that you endeavour to make up the time lost from the previous rotation(s).
It IS about flight safety. For me the vending machine is not particularly the issue - as mentioned earlier, the access to something more wholesome is what is required. I would not begrudge paying for this 'priveledge'.