To be fair, I don't think the idea wasn't without merit (We are popular among gamers + implementing a store = people will buy games from us isn't a fundamentally flawed equation), but as someone who used Discord solely for a particular purpose, I doubt I was the only person to see a game on the store, think "That looks interesting, except I'm just here to chat or whatever" and throw the game onto the "I'll get it when it's on a platform I actually use for gaming" pile.
Discord Store would be a thing for sure if Epic didn't star buying exclusives left and right. Discord didn't have that kind of money to follow them. So they dropped cut but as we know that was not the main reason why devs went to Epic Store.