It sounds that they were dishonest. There’s no way for us to know why. Sadly, you’ll run into these kind of employers.

I don’t know if I agree that employers don’t hire full time. Most people I know only ever work full time because they need income and benefits. Part time is only sustainable as a supplemental income.

If you need full time job with benefits only look for that. What you see is what you get. Doesn’t matter what they promise. Only go with what’s being given to you today and in writing