It's much easier to bug test and build for a PS5 as they are all the same. To get a resource intensive game working on PC means a lot more resources going into tweaking texture packs etc for a myriad of combinations of graphics cards processors and drivers and drives. Running on similar architecture is only part of the problem.
To be fair GTA V's PC port had a bunch of improvements over consoles and was very well-optimized with a bunch of settings. It takes time to make a good port.