Burnout is bad, but keep in mind that software development is a special beast. Some developers have streaks of productivity and procrastination. They may do overtimes not only to compensate in their mind for the time they’ve slacked. They themselves get f---ing tired of loops of wasting time doing nothing useful, and when they can they try to “just get this shit finally done”, because it hurts otherwise. It’s likely their own interest, not an urge to please you. Of course that isn’t healthy anyway, but that’s another story.