I agree, the prices are ridiculous. The main reason to buy a pop up is not price.
I see people using them because 1) they don't want to or can't buy a tow vehicle for a heavier trailer 2) the popup can be stored in a garage easily, which is mandatory in some areas managed by HOAs (not that any RV won't do better under a roof when not in use.)
Last summer a young family at a campground said they got a pop up mainly for the above reasons, but also because they found they had much more floor space and a better spot for a young child than their previous small trailer. They also had a cassette toilet.