I'm assuming GGP was not referring to physical therapy facilities however, some hospital inpatients do require that.
I spent 10 weeks as an inpatient on 6* daily IV antibiotics (which would have been impossible to do at home) to treat a serious infection in the bone in my foot. On some of my better days I managed to cover nearly 10 miles on crutches or in a wheelchair. Being able to use a gym to work out would have been better and substantially safer all round.
On the flipside, it's amazing how many doors one can get through using nothing but a lollypop-stick from the ice-cream machine in reception or a pair of crutches to open gates from the other side. And technically the "no public access" signs don't apply because you're not public, you're an in-patient at that point... but there has to be better ways of staying fit and sane that would apply to the other 99.9% of patients.