It needs to be “optimized” for controller input in exactly the same way. They could’ve chosen to budget for this “optimization” (whatever that even means) pre-launch.

I think the most likely explanations are 1) larger player base on consoles, 2) Rockstar wants to get the release cash injection ASAP, and 3) staggering platform releases like this prolongs buzz and even leads to a bunch of people buying the game twice.