The move is designed to make more titles Epic Games Store exclusive…
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.
It's almost like Valve invests their 30% cut into more than just CDN bandwidth and exclusivity contracts. They use it to build a compelling platform that people actually want to use.