A comment by 'vatueil' in this thread hinted at an important point: Steam is currently battling the massive library of half-baked 'crapware' that snuck onto the platform for the _sole purpose_ of being sold off as cheap keys in bulk. It's really more of a scam than anything.
Valve has a reputation to uphold, and it's no wonder they want to put this practice to and end.
It's a huge insentive to remain on platform despite other sales channels. It basically prevents competition, why build a steam clone when you can just build out the front end and let people use steam keys?
As a user I actually prefer it.
I already maintain a small handful of steam copy cats that annoy me to no end.
They're not doing very well there though. See any of e.g. Jim Sterling's videos about Steam over the last couple of years for excellent "Why are Steam sliding into the crapper?" commentary.
It did not passively sneak in, it was actively let in by Steam.
If I took two equally bad games-- one by a legitimate developer who may need some practice, and another by a developer whose intention is to scam the system-- would you be able to tell which is which?
I would argue that the former has a right to be on the platform (good luck trying to objectively define what constitutes a 'good' game, after all) and the latter does not. But there's no way to tell them apart until the devs show their true colors.
Seems fair to me.