Epic can't do that alone... it requires cooperation from and agreement with the game publisher.
Don't blame Epic for spending money to bring customers to their product. Epic aren't using shady tactics to do this, and Valve is free to do everything Epic is doing.
Also, as a game buyer, you DEFINITELY want a multi-source purchasing ecosystem; you definitely want to avoid a monopoly if the price you pay for games is important to you.
Exclusives are explicitly not multi-source. I want to be able to buy the games I want to play on the platform I want to play them on. This isn't always feasible, and that's OK, but it really grates when it's deliberately pushed in that direction.
