I don't know why this is a thing, but I have always felt it was wrong. I can't think of any other game (still running) that deletes player assets even when a subscription is still being paid. If that's a 'public service', imo it's a pretty lousy one.

I don't think it's asking too much for furnishing items to be saved along with your gear, minions, food, out-of-date event tokens, fireworks etc. If there's room to save all that, there should be room to save your furniture. I'd hazard a guess that the way they set up the timer and refund of purchase price has meant your furnishings are tied up with that. I would definitely like to see it changed though.
In the meantime, best to store any seasonal items on your retainer or in your apartment when they aren't in use.