For now, it's near impossible to me to replay games, even my most beloved game ever, GOW 2018, only finished it once.
That's actually very different I think. I have no problem playing old games if they still play fine and are fun, but replaying games I already finished is a different thing, especially story driven things like GOW you mentionned. I wouldn't really want to play a game like that again so soon already, but I would be more willing to replay stuff that is more focused on the gameplay / arcade style.
I for example loved NieR Automata in 2017, but I don't have any desire to play it again because I did everything in it and more, and even if I love the combats, I don't see myself going through the story and all the rpg progression again, maybe one day in a far future (although I doubt it for this example because I don't like route B in this game but that's a weird example), but if I were to find another old game, 10 or 15 years old, that had the same combats, I would totally be willing to give it a try. Playing old games doesn't necesarily mean replaying things you already beaten, and even if it does, it doesn't have to mean after a very short period, it could be much later when you forgot about most of it.
In the example of this thread, it goes back to the arcade / pure gameplay category I talked about. It's a lot easier to replay games like this because they are focused on instant gameplay, it's something you can start enjoying instantly without the need of "beating" it, just the fact of playing this type of game is providing enjoyment if the game is fun.
There are people that probably never played this episode of Forza Horizon and might be curious to simply explore a different map, or people who prefer the actual progression in this game compared to what Forza Horizon 4 and 5 did (where you don't have any progression and everything is unlocked instantly and you get a gold medal no matter what you do, this for example doesn't provide any fun or interest to me, the whole feeling of arcade scoring is completely gone in the recent games).
In my case I would be curious to play Forza Horizon 2 if it was on PC because I'd like to see the map of the game, as I live in the south of france, it would be funny to see that ingame.
Someone in this thread mentionned SSX 3 and I couldn't agree more, it's my favorite snowboard game ever, and one of my top 5 favorite games, and there are no more games like this anymore. The same goes for Tony Hawk, I love this series and it doesn't exist anymore. There have been "alternative" like Steep and Skate, but they are totally different type of gameplay which aren't what I'm looking for, so playing these old games is still the best way to get this type of experience.
There are tons of reasons to play old games.