1. There is ZERO reason for linking a PSN account to your Steam account for Helldivers 2. There's no cross-progression, so what's the point? The game runs fine without it. It's all about that MAU/data and being able to ban players at ease.
2. They releases the game on Steam in regions that don't even support PSN, so those people who didn't want anything to do with consoles, will now have to make a PSN account JUST to carry on playing their game, with zero difference. Problem is, they would need to make an account in another region and risk their account getting banned.
3. These are PC players. They want to run the game and not have to sign up to 1000 different services. Xbox does it well where your saves are saved on the cloud and you can play your game across any device. Sony doesn't do this for Helldivers 2, so there's ZERO reason to force players to link a PSN account.