Why havent they? Several first party sony studios have released next gen only games. none of them have even tried to do anything remotely close to Lumens and Nanite.
Epic doesnt make games but they've recently demo after demo with nanite integration. The first nanite demo is literally 3 years old now. They are so far ahead of everyone, it's not even funny.
Best thing for Sony, MS and all third party studios is to give up and pay Epic the royalties to reduce dev time and get the fucking next gen engine thats already up and running. These 300-400 person studios dont have R&D teams like Epic does. Epic has devs making entire levels in 3 days while Sony and MS are taking 5 years using last gen development tools.