i mean, I'm typing this message from Firefox which has pretty much a direct lineage to Netscape (1994), on an OS from 1991, using an instruction set which mostly comes from the 1970s
That's really not a great comparison, especially since browser-based social media and browser-based chat services (e.g. Facebook and its chat) are what killed services like AOL/ICQ, before later moving into mobile apps. Pigdin was fairly niche even back in the early 2000s. Facebook is bigger than any of those services ever were, because Facebook did a way better job or attracting the average person. My family used email before Facebook, for example.
Given all those things with hindsight, it makes perfect sense for browsers to have long lineages and it makes perfect sense why standalone chat services mostly died out.
And you assumed everyone who wanted a desktop chat app used pidgin and nothing else? Because there were plenty of "multi-service" apps. It's just that Pidgin was the more popular among Linux users.
Yeah, Trillian was, by far, most common among the general public (the non-programming, non-techy types). Honestly, Pidgin was pretty niche, I don't know of any non-techies that used it.
Multi-chat clients had limited appeal by design because non-techies were more likely to just pick whatever service was the most convenient to them. Seems expected that it would be the techie folks consolidating all their friends because they were more willing to use multiple services than the average non-tech user. Even Trillian was fairly niche by comparison, just far less so than Pidgin.
Pidgin's psychic mode plugin was great fun, though.
That said, it is annoying how so many chat services have gone out of their way to break the ability of 3rd party clients like Pidgin to work. :-(