It's the same kind of question like "Why would you want to hire people that don't want to do our algorithm puzzles/don't want to call themselves coding rockstars/don't have the same interests outside work". It's restricting the people you interact with along more or less arbitrary lines that are not a reliable indicator of quality/usefulness.

People like to frame it as "if they can't even figure out IRC", but that's a straw man. Nearly everyone can "figure out IRC", the question is if they want to bother with it when there's alternative things they could do.

(and I say that as someone who by far prefers IRC over every other group chat system)