Anyways...
This talk of Gran Turismo being ported to PC reminds me of
Forza Motorsport 6 Apex. That game was essentially a tech demo and a trial run for Turn 10 to develop PC ports of their (then Xbox exclusive) titles, and it wasn't without its issues. A year or two later we started to see new Forza releases head to Windows, and a few years later go on Steam.
Developing and optimising for the infinite combination of PC specs vs only 2-3 PlayStation machines (PS4, PS4 Pro, PS5) is a significant challenge, and I wouldn't be surprised if a lot of Polyphony's tech was built purely to run well on a PlayStation.
I hope Gran Turismo comes to PC eventually, but I can totally understand why Kaz is cagey on it, not withstanding the fact that even if something were in development he can't publicly say it until Sony do anyway