You must be well-off with well-off friends.
My friends would feel pretty bad if I were to pay for their hotel, and it is not an insignificant cost to many (especially since I'm living in the Bay Area).
Crashing on a spare couch? No problemo.
(Even if the economics of the spare couch work out in the favor of the hotel room. There is a utility in the spare couch beyond letting guests sleep on it, and that understanding takes away all the feelings of imposing, at least financially.)
However, all of that ignores the fundamental difference. You're not my guest when you're in a hotel. I can't wake you up for breakfast and make you coffee. We can't watch movies on the couch until either feels sleepy. And so on.
You can't rent the experience of sharing your home with someone if you don't have a home to share.