Helldivers 2 is different. The game already released, and then Sony tried adding PS Account requirement after many people had already bought the game.

Forza Horizon 5 has not released on PlayStation yet.

The Helldivers 2 things wasn’t that the game needed an account, it was because it was added on later. Its also different from games like Horizon Forbidden West or God of War Ragnarok because both of those are singleplayer games and should not require any kind of account to play the game as they do not have online gameplay.