Most likely because this was a star ship (or space station) with a limited number of personnel, all of whom have fixed duties that need to be done. You simply can't afford to waste your time away in holodecks.

The people we saw on screen most of the time also held important positions on the ship (especially the bridge, or engineering) and you can't expect them to just waste significant chunks of time.

Also, don't forget that these people actually like their jobs. They got there because they sincerely wanted to, out of personal interest and drive, and not because of societal pressures like in our present world. They already figured out universal basic income and are living in an advanced self-sufficient society, so they don't even need a job to earn money or live a decent life - these people are doing their jobs because of their pure, raw passion for that field.

The lack of capitalism meant that the holodeck program authors had no need to optimize their programs for user retention to show them more ads. So much fewer people suffer from holodeck addiction in Star Trek than are glued to their screens in our world.