Health insurance is available via many other sources other than an employer. It is (or used to be) an additional benefit, and an employer was not obligated to provide it, like paid vacations, personal days or sick days.
Coming from the businesses end of this subject, most of the restaurants have extremely high turnover, and the administrative aspect of providing benefits such as health insurance to a majority of part-time, second job, minimim wage earners (plus a little) is not in the realm of reality.
I must smile at those who feel cutting people to part time is something new.... it's not. It started long before the ACA. It's called being economically feasible in a economically tightened environment. It's just the media painting evil across the corporate world.