Steam

From what I remember, if you publish on Steam and other platforms, you are not allowed to offer bigger sales on other platforms. If you don't offer a similar discount/pricing on Steam in the coming weeks/months, Valve warns you about removing it from its storefront. And that's what's also written here.

Steam is the best launcher, store and gamertoolkit for consumer, I agree with that and especially since that I'm a GNU/Linux gamer. However that doesn't mean Valve is clean and has no cartel behavior. They make their money by create incentives for gamers to gamble on lootboxes.