Because the consumer is presented with correct info on the product page by the party actually selling the product - Valve. It's the same when buying a car - the information presented to you at the dealership takes precedence over whatever the manufacturer's website says, because the legal assumption is that you are basing your purchase decision on what is in front of you when buying the car by the party actually selling it.
> you will need a Steam account to redeem your voucher code.
This is an official page where Sony themselves sell the game via providing voucher codes for steam. You can buy the game here without ever visiting the steam page. This clearly qualifies as false advertising.
