When players are locked out of content due to lack of available in-game space then that content is very flawed.
Players should only be locked out for reasons such as lack of gil, gear, reputation, class levels, military ranks, etc. You know, stuff they can work on. You can't really do much work on getting a house if there are no plots left. On some servers it's simply hopeless especially if you're a new player.
Yes house flipping is an option but it's against the terms of use and it's understandable when players don't want to engage in something where they can easily get scammed, have no protection from it, and possibly face a ban if they're caught.