Because people need to eat and have a roof over their head. Choosing just one of these doesnt work for long.

As someone with two "real" jobs and two side jobs, it's because of interest rates. I can't afford my house unless I work more than full time.

On the plus side, my two main jobs have job security and benefits, so I'll be able to retire early since my pension will scale with my extra FTE. Or I can keep working to the usual retirement age and give lots of extra cash to my kids to start their adult lives debt free and with a head start on a house down payment. So, it's not all bad.