It would be a much smaller business model. My guess is that there have already been multiple market analyses of what you're talking about and the determination is most likely that the majority of hotel arrivals occur later on in the day.

This isn't to say a good amount of arrivals dont occur much earlier in the day, just not enough to justify the cost.

Additionally, to flip that would have hotel staff be cleaning rooms at a much earlier time (midnight to 4am), meaning they would have to arrive at midnight to start their shift. At 4am, the cleaning staff management would then need to spend a minimum of 1 hour to inspect each room to ensure it met company and legal standards. This is all ignoring the various tasks this can incur on the other staff like concierges.

I used to work as a Front Desk Agent, and later on a Night Auditor, in a small, but upscale, hotel. The housekeeping staff were some of the hardest working people I've ever met, and yet they were the least appreciated. Those hours in between check-out and check-in was always a hussle. I was always thankful I worked front desk whenever I saw them and would do them small favors if they ever asked (though honestly more often than not it was the other way around and I was asking them for some small request on behalf of the guest).

If we had the rooms available for an early check in, then we did it, but if not the best we could do was offer them to check their luggage in at the front desk and they were on their own until check in. The occurrence of this wasn't negligible, but given everything I witnessed, I determined, at least for our hotel, it wouldn't have been monetarily feasible to adjust that check-out check-in window to accommodate them. It simply didn't happen often enough to justify it.