Well, I can't speak for everyone, but I was out of the hobby, for 2 and half years or so and have no been back in it for about 6 months.
When I left the hobby I had just started a new job, and career, I was working insane hours and my tank became neglected. I had a tank crash, (my own fault), I watched my purple monster die as well as some other rare and expensive corals. Watching expensive corals, that you took the time to collect and care for, die is never fun.
If you don't have the time to enjoy the tank, and care for, then really it can become a stressor, and a giant money drain. I just said enough was enough, and I broke down the tank. Tanks do mature and become more stable, but they still require care, water changes, cleaning, monitoring, tweaking, upgrading, etc., but that is really the fun it the hobby.
While I was out of the hobby there was always an itch lol, I would see someone else's tank and get ideas, I would see a rare coral, or a good deal, but have no place to put the coral, wondering what my tank would look like had I still had it and it matured lol
So finally I bit the bullet and built a new set up, small, but I have always liked smaller high tech setups. I am glad I am back in the hobby, it is so relaxing. It is fun to collect and to try and set up the perfect tank. Now, I just remember to make the time, no matter what time it is to take care of the tank, recognize problems immediately and correct them immediately, of course experience always helps that. I don't regret it for a second, I love my new setup and I am very happy to be back in the hobby, and I throw the receipts away as soon as I buy stuff so I don;t know what I spend lol