I think it makes sense for Discord to stick to it's gaming niche, rather than trying to do a bunch of things poorly.
The other market is a bit more saturated, with Microsoft and a few others piling on top too. Whereas the Gaming market was completely lacking. There were a few clients which focused much more on voice (mumble, vent, ts), but nothing quite like Discord. Free and one-button to make a new server.
The only other contender I can think of is Raidcall, but that was a joke... Now there's Curse but they came too late to the market and were DoA, except the people they forced to use it by paying thousands.