Why are objects restricted to the ground only?

[sylly]

Why are some objects restricted to the ground only?

short answer? Likely to prevent unforeseen bugs

It probly wasnt any extra work to make these "restrictions". Housing items each have their own sub-class i.e. tabletop, wall-mounted, etc. And each sub-class has a part of the house they can go on. The extra work would come in allowing odd arrangements, like placing overly large floor items on a tiny table. They would basically have to throw out the whole current systems and make arbitrary decisions about how each item will interact with all the other items.

I think the housing systems is very well done with relatively few bugs (while the few that i'm aware of are actually pretty enjoyable). Hope this helps answer your question. Maybe if there were some specific items that you feel shouldn't be restricted to the floor, you could list them out and maybe say how you think they should work. The devs are always looking for ways to improve