Are you asking about holodecks on StarFleet warships?
Regulations. You only have X amount of leisure time. Plus, most likely, holodeck use is limited as well.
As far as "why would a civilian with access to his own personal holodeck ever leave", that's not really a SFF question. It's the same as any other addiction.
Some people wouldn't leave - there are people who starve their children playing World of Warcraft, after all. There are alcoholics and druggies. There are people spending 12 hours/day in front of TV. There are people asking 10 questions a day on Stack Exchange :)))
And then there are people who don't.