Instead they divide the playerbase, the game dies quietly (at worst) or slowly cooks until it's released on Steam and then it either does the same there or maybe they get the hoped explosion if it wasnt already on EGS.

Edit: Best case would be platforms dealing in feature exclusivity like SteamOS, Steam Deck, forums, mod integrations, groups, friends, achievememts, rewards (u points/steam points) for cosmetics etc. instead of dividing player bases.