Following the success of their staggered release strategy with GTA V, the reason it won't be releasing on PC is actually more of monetary reasons.
Why 2025? It is close to the end of life of the current gen consoles.
With the game not being released on PC for a year or 2, it makes those who can't wait to rush and get the console versions because there is no firm date for the PC version.
Following with a year or 2 of wait, they'll release it on PC. Gaining even more millions of sales from those PC users who didn't buy it and those who has the console versions but wants to get the best graphics and performance out of the game.
With the release of the next gen consoles, they'll release yet another remastered version that either has to be paid in full or might be as an upgrade for current gen console owners. We'll never know.
Nevertheless, GTA V sold over 180 millions copies while all previous entries sold around 20 million.
That is why Rockstar will aim to repeat this same marketing release strategy that works so well with GTA V with the upcoming GTA VI.
So you can see how easily they can sell millions of copies of the same game year after year just by releasing it on different platforms all without losing the hype created from the initial launch. It ensures constant revenue just from that same 1 game like what they did with GTA V releasing it close to the end of the PS3 + Xbox 360 era.
That's the only reason why they'll release it in 2025 and not any sooner.
GTA V Release Dates
PS3 + Xbox 360 - 17 September 2013
PS4 + Xbox One - 18 November 2014
PC - 14 April 2015