Epic Games Store is offering developers 100% of revenue for six months of exclusivity
(www.videogameschronicle.com)
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.