The fact is, Discord as a platform is more accessible compared to IRC.
Guess it depends on what you mean with "accessible". In terms of accessibility for impaired users, IRC is a open protocol vs a service that disallows 3rd party clients. I'm sure there exists better options for IRC than Discord, and at the very least, IRC allows you to access it however you want, be it visual, textual, voice control or whatever.
Besides, Discord being a US company, need to prevent users from Cuba, Iran, Syria (and NK) and is also banned in a bunch of countries like China, UAE and Egypt. So in that sense, Discord seems less accessible than IRC.
Only remaining part is that Discord has a somewhat easier "getting setup" UX than IRC for younger users, as it's more similar to the type of services they're probably already use.
(Sarcastically saying something is interesting is something I find distasteful.)
Anyway the irony is that the project chose to use a discussion platform which uses lots of modern web cruft and would be a big challenge for a new browser, when they could have chosen a (maybe less capable) simpler platform like IRC or some simple web forum which would more likely have run on Ladybird.