Technically, the barrier to entry is as low these days as any other messaging service: you can sign up on IRCCloud and instantly have a friendly browser-based experience without worrying about setting up a persistent client, logging etc. by yourself, and mobile and desktop clients are available.
These days the network effects just favour old farts and engineers.
Also I like the barrier to entry IRC has, it keeps the worst of the worst out because you need some technical skill to even get in. That's why most programming language / distro channels on IRC are of better quality than random slacks or discord servers.