Perhaps the room just isn’t used very much and doesn’t get a lot of attention. Or perhaps they only assign it as an upgrade on one night stays, and it’s rarely paid for (or hasn’t been in a long time), and so on one night stays no one bothers to complain – they’re leaving anyway. So without guests letting the hotel know about maintenance issues, those issues don’t get addressed.
I fell victim to this myself – I didn’t stop at the desk on the way out, so didn’t complain about the condition of the room.