They aren't, but the hotel doesn't charge you extra for leaving the lights on, so people don't care.

Right. The marginal cost to the customer for leaving the lights on is literally zero, so they have zero care about it.

This is why modern hotels have you put your room key in a slot that enables the lights to go on. When you leave the room, you take your room key, and the lights go out.

Evidently, people leaving the lights on is expensive enough to justify these key light switches.