Surely if a person was too ill to receive ANY visitors when they were too ill to go to jail, they are definitely not fit enough to fly. Of course there may be also concern they are a flight risk. I can't imagine why.
Flew Thai earlier this year. We were very disappointed. Went to use the toilet and it was clear somebody had been sick. I went to tell a member of cabin crew only to be told that they had cleaned it already. Vomit still on the seat and the floor.