The chat services enable responses, by making it low friction, by giving the feel of being informal and real-time in a way that email and forums don't. They also enable asynchronous responses by being persistent, that your message won't go lost and unseen by a moment without network connectivity, unlike IRC. They also enable responses by being cross-platform and device-independent, unlike SMS. They also enable responses by centralizing account control of who participates, so users can join a ready-made group organized by an administrator, unlike say Facebook messaging.
Users seek maximal interaction. The Slack/Discord model achieves this by supporting both synchronous and asynchronous responses. The former requires an informal real-time interface, the latter requires persistence. That's what came together on these services that hadn't before.
I used to routinely go back through the day's discussions in #general and #need-help whenever I got home from work, and yes, reply to questions that had been asked 8-10 hours earlier. But, Reactiflux has become too high-volume for me to be able to do that.
That said, I still will scroll back in some of the lower-volume channels to see what came up. So yeah, having chat persistence is an incredibly nice feature, and I can't imagine doing without it.
Chat channels give immediate and interactive feedback. When someone asks a question in Reactiflux, they frequently get an answer within minutes, if not seconds, and we can iterate on asking for details quickly if needed.
The downside is that multiple simultaneous conversations in the same channels quickly become hard to handle, questions can get missed if they're not answered right away, and we do see a lot of the same questions over and over.
I know the Spectrum folks have emphasized the searchability of their site as a major selling point, both from Google indexing pages and the ability to search for existing threads. I won't say they're completely wrong, but at the same time, my experience is that newbies in particular won't actually search for existing answers - they just want to ask and have someone answer directly.
I scroll back and check for reported bugs and any problems people had that weren't resolved by others.
"They should just ask on a forum/github/stackoverflow" you might say. Ok, but they won't, they'll just stop using my library instead.
Forums require too much risk. Spend 20 minutes crafting a question, never get a response. Github and Stackoverflow are far too complicated for the average user. What's an issue? What's a template? What's a minimal reproducible example? They just want to know what error code 501 means...
It's the same as just barging into a conversation a group of people are having. You don't want to just join and start talking about a completely different topic. So you join, and wait for a bit to get a feel for what they're talking about before piping in. But with IRC, sometimes it can take _days_ to get that amount of information, depending on how active the channel is. The same thing could easily be accomplished by being able to read the last 10 messages in the channel.
When I go online in Discord I don't read up the last few messages unless there's a particularly interesting discussion going on.
It exists.
And remember that IRC has been around since 1995, when the idea of separate protocols to do different things was common place. IRC has been dying a very, very slow death.
(and despite nostalgia: IRC was never big. Even the largest of IRC servers only had around a hundred thousand users. That might sound like a lot, but we're talking globally: the most popular IRC server had a fraction of the users that CompuServe did, and CompuServe was decidedly worse at being a chat system, even though that was the main reason you'd use it)
Simply by being in an IRC channel you become part of that, which is radically different from any of the other media you mention, where one has to actively go through the records (as it were) to get an idea of what's going on, and what the shared culture and body of knowledge is.
They really are very different media with a very different experience, and today the only experience that has managed to recreate the value that set IRC apart from other communication tools is Slack/Discord.
Minor nitpick: 1988 to 1993, depending on what you consider 'irc'. (1988 for irc1, 1993 for the standardization of ircII that still defines irc today, 1992 if you consider the efnet/undernet fork to be the birth of true irc).
But seriously, I don’t understand why persistence is such a huge deal to people. Chat is for transient chat - it is meant to be non-persistent just like verbal communication.
There are so many mechanisms for persistent messaging (forums, text messages, emaills, and everything in between), I don’t understand how an entire industry spawned from a concept we already had?