I agree, Sony had little to no reason to even release a midgen console, while MS felt that they had to release something significantly better.
I would argue that only Sony had a reason. They designed the Pro for PSVR. They knew the original PS4 was under-powered, hence the release date to coincide with PSVR. MS made a "me too" console. The design is basically a PS4 and they were a year late to "mid-gen". Of course they had a chip on their shoulder over power too.