You're more than welcome to have 2 houses if you can. One for personal and one for FC. Then you can have an apartment and a FC room. So technically 4 "houses". This is perfectly fine and if you want to rent your house you're more than welcome to. When I joined it was easy to find a small, medium or large plot of land but of course things change lol
I think that SE is in a bind now that the population is pretty high. They can't just add more servers, it's expensive for such a small part of the game, although admittedly I am a fashionista of sorts that decorates homes a lot. I even look at youtube videos and visit various websites to see other people's creation, it's a way of life! But I can't do that right now because the login queue makes it impossible to swap between alts.
Anyway....... There's nothing wrong (in terms of the rules) with buying land and doing nothing with it. You're given the right to do it and it's your right to squat on property if you like. What you're not allowed to do is sell it for real money which people have done. I've heard people selling their small property for over $1000! It's crazy. Morally I think it is wrong to buy a piece of land and sit on it but you never know the reasoning behind it. Maybe they can only play 1hr a day or every few days and eventually they plan to make a house and decorate but don't have the time/gil for it yet. The land itself I believe gets taken away if no house is built within a period of time. I could be wrong but I think you have a week or two to do it. I spent over a year in subscription fees just to login once a month to prevent demolition while I was on hiatus. It shouldn't be that way but it is. Maybe this part of the game, SE will eventually figure out a more cloud-like way to load the instances to alleviate the need for so many servers on this feature. One could hope.
Edit: I meant to say that I had made a suggestion years ago about having your own instanced island where there would be no need to load server resources unless someone was there. I think they will be including something like this soon but I don't know if it will come with a house or if it's just farmville.