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.