In my experience it's because of two things mostly. (1) Naming generics is harder than naming other variables for whatever reason. (2) Signatures with generics

In my experience it's because of two things mostly. (1) Naming generics is harder than naming other variables for whatever reason. (2) Signatures with generics in them are stupidly long. Signatures with generics tend to be super unaesthetic, and oftentimes unaesthetic code is conflated (correctly or incorrectly) with bad code.