Obamacare mandates employers offer healthcare to people working 30 hrs a week. A lot of places will only allow you to be scheduled for less than 30 hours a week, even if you are able and willing to go full time. It's stupid, but some people have convinced themselves that it's Obamacare's fault that their employer is shitty and the subsequent governments have been unwilling to close that loophole. It's also worth mentioning that employers did this even before Obamacare because there are other things that full time employees are entitled to that part time employees aren't.