Couldn't agree more. The pools/hot tub should not be closing as early as they do. I'm a night owl myself (I'm posting this at 1:30am on a Sunday night, after all) and it sure would be nice to use them late at night. - especially the Quiet cove area. Midnight - when the OP's pics (which are great) were taken - is not late by any means. At least, i don't think so - especially when on vacation. So I find it remarkable how much of a ghost town the ship is by that time. I've certainly encountered the same on our cruises. I usually deliver our FE gifts in the 12-1am time frame and I almost never encounter any other passengers.
I also agree about Royal Caribbean cruises (we've been on two - Freedom & Oasis), and it's not just about the pools. While although I am a night owl, I'm usually not one to spend the nighttime in the bars or nightclubs (I prefer the casino, actually). However, just walking around an RCCL ship at midnight, or even 1-2am, there's always at least some signs of life - and not just in the casino. There's always people walking through the Promenade (a design feature I really love on their ships) as they head to the (24-hour) cafe or pizzeria (which I believe is open until 3am nightly), or just passing through. If you go up to the pool deck and walk around, you'll still see some folks - maybe not a lot, but some - hanging out or also taking a stroll themselves.