“Right to work” refers to the fact that in those states, unions cannot force membership or payment, or force you to participate in labor strikes. You can still have a union in those states, but it’s very difficult for them to be effective because most people will choose not to pay into it, and strikes have significantly less bargaining power if there’s no legal obligation for union members to follow through with a strike.

The result is that in such states, there are very few unions, and so very few protections against firing workers for arbitrary reasons.

It is also the really easy to leave states. When my old company was taken over by new owners, a few years down the line someone was leaving to go work somewhere else. They gave their two weeks notice and was fired on the spot. Next guy that went to work elsewhere just quit without notice as they already knew they would not get their two weeks.