You need a reasonable financial buffer (or at least good credit) to be a homeowner to cover the large expenses that invariably come up. If you're not handy and need to call professionals for every minor repair--well, though service calls will add up quick.
Sometimes people need to change their housing circumstances in a hurry (e.g. bad break up or bad neighbor) and negotiating two real-estate transactions would be time consuming.
In short, there are lots of good reasons people don't want the burden of being a home-owner, but still need a place to live. Someone has to own and be responsible for those places.
