1/ each additional employee comes with additional costs: management, communication, onboarding, HR, office space, etc..

2/ People in a 40 hours contract usually work more than that. Employers can try to seek out employees that don’t mind working more than paid for.

3/ People who’d look for 80% jobs are (from employers perspective adversely) selected to be people that will monitor their hours worked and not give away their time for free.