> Thus, the original first reason can't be popularity -- because there was a point when Discord was not popular and it was still chosen over Matrix & IRC. The reason is that it's easier for project maintainers to create new Discord servers + channels.

Matrix did not have "servers" (in the Discord sense) until very recently. It's also much harder to produce an open, federated protocol than a proprietary one so Matrix has been less featureful than Discord for a long time, but the gap is closing quickly.

There's also the matter of marketing: Discord is a product, Matrix is not, thus it's harder to market. Yes, now there's Element, which is a product, but given above, Discord has had an effective head start of several years.

Give it a bit more time.