One thing to note there is GT6 selling (relatively) poorly. Why did it do that? Because it was releasing on an old console when a new one was already out, and because of that wasn't revolutionary in any way. It was mostly just GT5 with a bit more content. Players were already moving on to PS4, and didn't want this sub-par game.Well, assuming they are really going to PS4, I think I may see their thought process.
According to the most recent available figure, the PS5 has sold 7.8 million units worldwide. Main GT releases have only sold under this number once: GT6. So there's probably an expectation of the number of copies they will want to sell. Then we have to take into account that, included in those 7.8 million, are scalped consoles, which even though count as sales, may not be in the hands of gamers yet. We also have to take into account that not everyone of those 7.8 million are going to be into racing games. Finally, we have to take into account the fact that access to the PS5 will still remain difficult for a while, as production tries to keep up.
All this to say that, if you stick only to PS5, you have a maximum of around 7.8 million potential users. Add in PS4 and you have another 100 million potential users, give or take. Go one step further, add Steam, that's another 20-30 million, perhaps.
It always ends up in a numbers game.
Also a thing to note is Spiderman Miles Morales selling more on PS5 than it did on PS4, and there were way less PS5s back then than there will be in 2022 (or whenever) when GT7 will release.