Are bad teachers created because it is nearly impossible to fire them after tenure, or are they created by poor acting students?

There is always the debate about bad teachers, the ones who are apathetic, don’t teach, show no compassion, belittling, and seem to have no interest other than showing up can getting their check. What makes or create bed ineffective teachers? Because they know they virtually cannot get fired after they make tenure they get lazy and uncaring? Do they get uncaring because too many students are rude disrespectful and don’t care to learn? If there were no tenure or it was harder to get, would there be better quality teacher across the board in general?