Couple of reasons to dislike the epic store.
Epic is half owned by by a Chinese company and is beholden to their whims.
Epic is entering these exclusivity deals explicitly for the purpose of denying access to these games on platforms like steam. PC is supposed to be the open platform, not the platform of exclusives and consumer hostile moves like this. Epic is introducing something to the PC space that should never have existed on the PC space.
People put games exclusively on steam, not because Valve is an anti-competitive monster, but because Valve has made a good store. People like it. And it is easier for a developers to do that instead of selling their own.
However, Valve is so incredibly open that you can literally buy games for steam not on steam and own the games in two platforms by using humble bundle. All over the place you are able to purchase games from developer websites and get a steam key for free.
Epic games is an exclusive monster that can and will suck down the entire computer game playing space and annihilate every possibility for there to be real openness and competition in this space anymore.
If you are using the epic game store you are contributing to this and you will be to blame when they inevitably cobble up the market and lock you out of being able to do anything but hand them money.
Then they will hand your gaming data to China because they are half owned by tencent.