While it's true that you can't back up with a towed vehicle, the advantage of the RV is that you don't have to -- only takes a few minutes to pull the pins and free the car and generally when I'm towing the car, I want to use it, so I'm going to unhook it anyway when I park, may as well unhook it before I back in the space (especially since I typically want to back in all the way and put the car in front)

But as you say, different use cases for different people - if you already have or want a truck (or other tow vehicle), a towed RV makes a lot more sense. But I don't want a daily driver that's large enough to be a tow vehicle and it makes no sense to buy a tow vehicle that's only used for towing.