They used IRC but they switched because IRC is just too inconvenient. Discord is proprietary, but it works really well for them. They chose to be pragmatic.
I get that Discord is more practical, but it is at the cost of freedom, trustworthiness and privacy. Communication platforms are the last place you should compromise on this, since your choice is directly going to affect the choices of many others.
There are tools which are much more user-friendly than IRC (and even Discord, in some aspects), such as Matrix or Zulip. They easily enough could’ve been more pragmatic picking those instead.
There are tools which are much more user-friendly than IRC (and even Discord, in some aspects), such as Matrix or Zulip. They easily enough could’ve been more pragmatic picking those instead.