The total cost of servicing that room is going to be extremely similar regardless of a few hours difference in the person physically being in it. They still nee

The total cost of servicing that room is going to be extremely similar regardless of a few hours difference in the person physically being in it. They still need to check you in and out (potentially involving a person, though not always), they need to change the room the next day, and it's still not available to another traveller (granted that doesn't exactly apply to a last minute booking like this). Maybe they'd use a bit less electricity but I doubt that's a significant part of the cost. They'd also probably not have a shower but there's no guarantee of that from the hotel's perspective.