that's not really what's going on here though. Epic came with the last minute bag, and paid for one year exclusivity
competition would be the game being on both stores. they're selling the game for $10 cheaper on the Epic Store (although the Epic Store's lack of diverse regional pricing means some countries will end up paying even more for the game then they would have on Steam), so that could have been enough incentive to get a lot of people (not me) to buy the game from Epic
they've also put themselves in this weird situation where they still have to support the game on Steam because of pre-orders. playing the game on Steam is a pre-order bonus now
I'm sure everyone involved knows they will get less sales on the Epic Store. whatever bag they got is supposed to compensate for that. but it remains to be see if it will be 'enough'. they've definitely created some bad publicity and ill will. I'm not sure if they underestimated the negative reaction, but it's another reason it seems so crazy for them to make this move so close to launch
I don't condone this behavior, but the review bombing has already started... (this is from the Metro 2033 page)