Why should that not be more of an expectation? Sony has started putting out formerly PlayStation-exclusive first-party games on PC. Even Bloodborne may show up on Steam soon if rumors are to be believed.
It would be a good thing if Half-Life Alyx came out on other PC game stores, in exactly the same way that it would be a good thing if a game like Control came out on other PC game stores. Our expectations are socially constructed and we should question them more.
Look I think they’d sell more copies and it’d be good for everyone to have the content more widely available but it’s not always feasible to require it. A PlayStation game doesn’t just automatically work on PC and it probably takes numerous hours to get a PC game ready to submit to the Steam store. I’ve certainly wasted many hours localizing text for iOS app submissions and the like.
With so many different stores to download apps, it gets increasingly unlikely anyone is going to take the time to cross list on all of them.
If we wanted to change how this worked, I feel like we’d need to consolidate on fewer marketplaces. For example, apt-get has access to a huge variety of packages so I don’t find myself using the Ubuntu App Store or random third party marketplaces as much as I do with games.