Given the attendees, I'm surprised some didn't seriously mess with anybody entering their rooms. At the very least, one would expect all the goons getting doxxed, their phones pwned, and the whole shaming posted somewhere.
This, and it's not about DEFCON, or conventions in general. I stayed at TI a while ago, and didn't have housekeeping come in my room for 3 days (I honestly just don't like people in my room). Eventually they did send up a security team to knock on my door. As soon as I answered and talked to them, they just went away and were happy I was alive. But this is a new pattern by Vegas hotels since the Mandalay Bay shooting, this has never happened to me in many years of Vegas before that.
I think if you just randomly visited Mandalay or Caesar's on vacation, you'd have the same likelihood of having your room looked in on. Every room has a notice to that effect now.
This isn't exactly true. If you tell them you don't want housekeeping service, they insist on having a staff member check inside your room at least once every 24 hours. If you're OK with having your room made up, they weren't searching rooms. I had no problems at DEFCON because I like having my room cleaned.