The Epic First Run programme allows developers of any size to claim 100% of revenue if they agree to make their game exclusive on the Epic Games Store for six months.
After the six months are up, the game will revert to the standard Epic Games Store revenue split of 88% for the developer and 12% for Epic Games.
The problem is that none of these other launchers offer features like Steam Input, Proton, or the Workshop. Steam competes by making their platform the most attractive to customers. EGS competes by making their platform the most attractive to publishers. At the end of the day though, the publishers have to go where the customers are.