They're gonna eventually want to update the online multiplayer, and that would can be done with a new game.
Not to mention that increases their revenue a lot more, as it not only gets more folks interested in the MMORPG, but they'll buy the new game as well. A smart idea would be to set the game in another city in San Andreas, and connect that map to GTA5's current map for the online multiplayer.
Fortunately, KOTOR, Forspoken, and Uncharted are all confirmed to be coming to PC in addition to PS5. Forspoken I'm especially happy about because I liked the look of it but not enough to want to buy a PS5... assuming I could even find one given the stock still isn't quite meeting the demand.
Good riddance on Sugiyama. While I’ll respect his contributions to video game music (despite in not appealing to me personally), that man had so many awful viewpoints. I’m not actively jumping with joy but I feel nothing for his death.