Minimum dimensions for parking bays have not been updated in years. Cars have got bigger.
I'm not advocating parking in disabled bays as standard practice, but I can see how the problem has arisen.
On the odd occasion I go to the local supermarket, I will either:
a) Park in the furthest corner of the car park and take up two spaces; or
b) Park in whichever parent & child space is furthest from the entrance;
I am not interested in taking up gymnastics to get in and out of my car just because the bays are all so narrow that there's virtually no space in between cars.
PS if there's multiple disabled bays at the gym and they're all empty, I'm not going to lose sleep over somebody parking in one of them. I do agree however that if there's only a couple of these spaces then it's not really on.