Maybe it's part of their recovery process?
Depending on the nature of their illness it very much can be, and can be encouraged - the socialising or going out and about, not the SM aspect, by their doctors. Also can be dependent on the type of work they do.
I have had a small number of incidents where I have been off work but still able to be out and about:
2 ops around 14 years back, 2 periods of 7/8 weeks off work in relatively close succession. Wasn't safe to be at work, due to the nature of the job, but encouraged to try and go out and about increasingly in order to aid my recuperation.
A bout of pneumonia about 9 years ago - off work for 7 weeks. Again, not able to work and had to take it easy but encouraged by doctors to work up in steps to going out and about and they sanctioned a pre-planned holiday near the end of the time off as being good for my recuperation.
About to have a medical procedure in month or two's time which will need 1-2 weeks off minimum. If the date stays the same as a newly arranged date I will be going for an evening family meal out including a hotel overnight during this time. I will no doubt have some wine during that evening. My consultant has already said that will be fine to do, and I should be up to doing it, but not yet able to return to work.