They got paid for the exclusivity, after that if they don’t sell as much then so be it, but just releasing on Steam is like choosing to play the lottery as a retirement plan and signing an exclusivity deal is like having a job, one might pay tens of millions or nothing, the other you’re sure will let you buy food for the next couple of years.
There’s tons of games on Steam that the devs have put everything they had in it only to never see any success and then you’ve got games like Vampire Survivors where nothing happened for months until suddenly a YouTuber started playing it and it became a major success. And I mean, good for Luca (and eventually for his team), but for every successful small dev there’s tens of unsuccessful ones…