Discord "won" because it's literally burning cash and offering a service for free (for example, I don't have to pay for a t2.micro instance to host a Mumble server). But this is obviously not sustainable.
If you're selling a dollar for fifty cents, it's not hard to find a market.
The price wasn't the issue (imo), it was simply the user experience. It had the best, by leagues. Users (ie, non hosts) didn't pay for any of these products, but the UX of Discord was vastly superior in my view.
I'd rather install something compared to using the "webapp" version if it used 30 MB of RAM rather than 3000MB.