9 months may seem like a long time, but it really isn't. I left this game for a bit over a year and came back, and that's nothing compared to how long I left, say, DDO. Things happen, people move on, and they sometimes come back. They'll want a house if they had it, and it's an incentive for them to come back to the game and play again if their house stays. If their house disappears, they'll be less likely to come back.
This would hardly be an issue if plots weren't insanely limited. There are 1440 total plots in the game. Right now, there's 6,545 people playing the jumbo cactpot. These numbers don't work together.