Valve does not limit you in where your game is sold, the publisher of the game has to set this and the publisher for Helldivers 2 is PlayStation Publishing LLC.
Partially, with the PSN account “requirement” for multiplayer (which worked fine without it even with cross play), they also banned 176 countries from getting the game, accidently (not really) those are the countries where PSN is not available. This Steam store ban is still not lifted to this day, they only reverted the PSN account “requirement”. And before anybody asks, no it was not Steam that did this on their own, it is the game publisher (PlayStation Publishing LLC) that has to restrict game availability.
Wait, is this the same company that installed a rootkit on your computer when you inserted a genuine bought music cd, or has had their databases breached several times, where plain text user credit card data was stolen and the latest one was not that long ago.
Sony finally surrenders: PSN accounts will be 'optional' for games on Steam, but they'll give you free stuff if you sign up (www.pcgamer.com) angielski
PlayStation Uses Safety Concerns To Defend Steam PSN Account Requirements (www.thegamer.com) angielski