This is incredibly reductive and at best looking at mumble through Rose tinted glasses.
Mumble has had a rocky past as a useful piece of software and it's absolutely not been a discord competitor any more than TeamSpeak is a discord competitor.
Maybe it's changed recently, but mumble has not had the feature set that made discord useful in the first place.
That might be true, but claiming that people only moved because they were propagandized into doing so by a for-profit company is absurd.