>I can't comprehend why this isn't widely used.

Maintaining the DHT connection is "expensive", expensive meaning a few packets a minute. That means mobile clients can't enter sleep and stay connected, (without corp backed push notification services. Which we can't use/trust) So it'll kill expected battery life on mobile. Add to that, multidevice isn't supported, (I implemented the feature, but it didn't get merged before my will to work was killed by trolls) and Tox can be a bit frustrating to use. :(