People don't want "a distributed platform that isn't irc", but a platform they like. IRC fails primarily due to requiring a persistent TCP connection, and secondarily due to not supporting image sharing, and tertiarily, due to not supporting emoji reactions.

Requiring a persistent TCP connection is simply a complete dealbreaker on the mobile phone platforms which make up, like, 90% of computers in existence. Fixing that would go a very long way, but it requires a lot more server-side storage since messages must be stored on the server until a client reconnects.

Data privacy requirements go along with server-side storage. If messages are stored for a few minutes that's probably okay, but that's too short to implement the feature. If they're stored for weeks, and especially if images are stored, then for legal reasons there must be a way to moderate them. On another front, at least the server only needs to store one copy of the message for as long as the slowest client might need it; it might as well just store the entire channel history for a fixed time. These considerations lead to a design like Slack/Discord/Mattermost/etc, and trying to make it decentralized leads to a design like Matrix.

You may think of IRC bouncers which don't have these issues, but notice the responsibility structure of an IRC bouncer is completely different. With a bouncer, the responsibility for storing the message lies with the reader, not with the network, so completely different considerations apply.

Sharing images and videos is just useful sometimes, even though 90% of the time it only serves to increase spam. And I don't get why users are extremely horny for emoji reactions, but they are. A platform can exist just fine without either of them - every social platform develops a unique personality in response to the constraints and nudges the platform imposes on users - HN doesn't have images, videos or emojis and that's a good thing for HN. It's the persistent connection thing that's the real killer, because it means the platform is simply unusable 90% of the time.

A version of IRC tailored to slower connections might look identical to (the non-binary segment of) Usenet. However, even Usenet has light moderation, that differs per server, to avoid being clogged with spam and binaries.