Apart from the (more than obvious) technical feats, they've raised a lot of money and can afford to offer all of their services, some of them a bit expensive, for free. If they can't find a way to monetise, though, they'll be in trouble.
Had TeamSpeak or Mumble been able to offer hosted services for free, maybe Discord wouldn't have existed.
They have pushed monetization recently. Discord Nitro went from custom id, animated avatar and all emotes of all your servers everywhere to a game subscription service (obviously while raising the price)
Besides a bunch of lootbox stuff for the kiddie shooters, there is Civ IV, XCOM:EU, Bioshock 1&2, Metro 2033 Redux, Project Highrise, Metro Last Light Redux, OOTP18, Tyranny, and so on.
Most of those are not for me, but Indie rubbish seems a bit off.
Had TeamSpeak or Mumble been able to offer hosted services for free, maybe Discord wouldn't have existed.