Let's think about it for a second:
- you cannot have anything (unless it's flat, so maybe a book on a table) on those mebels if you want to lower the bed
- you also need to make sure nothing is around to block your bed
- you cannot use the wall at all since it's part of the lowering mechanism
- you need to fit this whole contraption inside
- there must be some additional lines holding the "inner" end of the bed otherwise it would fall apart
- having a heavy mechanical contraption right above my head doesn't really induce a feeling of safety
- it can get stuck up, so you are left without a bed
- or even worse, it can get stuck halfway through descending, so you have no room left in your room
Incidentally, a good folding couch has none of the aforementioned problems.