One other factor: I think there is something selfdestructive in FOSS projects in general thanks to large amounts of incredibly loud feedback focused around the strong opinions which predominate FOSS communities - which very often pull directly in the opposite direction to building a usable polished app like Discord.

Stuff like “Matrix is crap because they didn’t make it E2EE from day 1”, or “Because servers store metadata” or “Because it didn’t have a legally registered foundation at first” or “Because Element’s default config points to the Matrix.org server” or “Because Synapse supports shadowbans” or “Because the Element apps influence the direction of Matrix” or “Because it’s not XMPP” etc etc etc. It’s surprisingly hard to keep focused on building apps that optimise for mainstream users when the loudest voices are campaigning to optimise for their own crusades. I suspect the same effect has substantially negatively impacted Linux on the Desktop and other places where FOSS usability has failed to punch its weight against mainstream usability.

On the other hand, there are quite a few examples of FOSS apps which have successfully pulled themselves out of this hole of being “built by geeks for geeks” into being successful and even delightful to a more general mainstream audience: Firefox, GitLab, Blender, Audacity all spring to mind. And that’s the model we’re trying for at this point.