That really sucks, sorry to hear you lost your prized house.
The rules basically boil down to an arbitrary decision on the dev's part. They picked that because it made the most sense at the time to help others get access to the system. It isn't unfair by any account, nor is the availability system flawed like many people like to complain about. It's actually working exactly as intended. But it is true that the 45 day limit is short enough that real life can dictate whether or not you get to keep your house. Especially in these covid-19 days where people can get stuck abroad with no access to the game. SE generally do a good job of turning timers off for global/local crisis' though.
This is just going to be one of those hardsh "live and learn" experiences. Better luck next time.