Epic is paying boat loads of money so they don't have to compete, that's the issue. Their store is objectively worse than Steam in almost every way, they know they can't compete, so instead they're throwing money at the publishers and telling customers to suck it up and use their store, or don't play the game.
You think Epic is the only game store that buys exclusives? Sony and Microsoft have both been doing this for many years for their platforms (whereas Nintendo prefers to simply develop their own exclusives instead of paying third parties for them).