People buy cases because they feel their $1,000 slab of metal must be protected.
For me, it's just not worth it. Had iPhones break while on trips and it's just an absolute hassle dealing with replacements, especially when there aren't Apple stores for hours, while I can just put on a protector and done.
(Plus I think a clear case looks really nice and brings a retro Casio vibe.)
I didn't get a case when I bought my 15 pro.
For two weeks I was without a case, dropped the phone two or three times.
Screen got scratched in 3 places and the paint chipped from around the bazel.
Went into a store and got a case.
Same camera hardware as the flagship 6s, but more comfortable to use one-handed and the camera lens was flush with the back.