You are correct that a TT is way more bang for the buck.
I think it's because the folding hardsides are a relatively low volume unit. They have a lot of "special" components that are probably higher cost per unit.
IMHO the main reason people get them is their low weight. I looked at them pretty hard, but was deterred by 1) no private toilet area 2) lack of a shower & water system in most models 3) the lack of available storage when folded up.
They might be OK for 1 person who would be happy to be alone using a porta-potty and washing in the sink, and there is probably enough folded storage for 1 person's food and belongings. But that's about it.
If I'm going to buy a camper I want a private toilet and shower, and the ability to keep it loaded and ready to go for a trip.
Single empty-nester in Middle TN, sometimes with a friend or grandchild on board