It was a little bit of everything, really. Discord exploded in popularity because:
1. Its free functionality was more generous than many comparable services. Nobody wants to pay for a Mumble server.
2. Its UI and audio quality and noise cancellation settings put much of the competition to shame.
3. Only needing one account for every Discord server in existance gave it the same kind of appeal that let Reddit/Facebook kill off most individual forums.
4. Good marketing, which gave it the critical mass of users and hobby groups that it needed to succeed initially and now make it harder to move away from.
1. Its free functionality was more generous than many comparable services. Nobody wants to pay for a Mumble server.
2. Its UI and audio quality and noise cancellation settings put much of the competition to shame.
3. Only needing one account for every Discord server in existance gave it the same kind of appeal that let Reddit/Facebook kill off most individual forums.
4. Good marketing, which gave it the critical mass of users and hobby groups that it needed to succeed initially and now make it harder to move away from.