> Wrong. Stores need traffic...
That's incredibly reductive. Not all traffic is created equally. Reddit, for example, is notorious for providing awful bang for your ad buck[1].
> Discords user base is traffic.
Oh, I see, so Facebook and Google should've started online stores because of.. traffic? Of course not. If you build a (big enough) platform for free, one of the few viable ways to monetize is to do ads. Making a store is a very dubious prospect (which has not been received particularly warmly). If you're going to bring up Steam, keep in mind they had about a decade of first mover advantage.