No. I don't have an ideology here. Just facts I'm sharing.
"They didn't care because they were elitist."
Do you have proof of that so called elitism? Maybe they didn't want to get into a holy-war. Maybe they didn't want to break a 30 year old protocol.
I think, they didn't care because they just simply didn't care. Don't confuse elitism for general apathy.
Also, have you looked at Mattermost?
They get into holy wars, break stuff, and take action regularly. So there goes three reasons. What they will do is call people idiots or lazy if they complain about poor UX. Or remind them how you only do (arcane steps here) to accomplish the task so why the fuss?
It's hard to absolutely prove elitism over all other things that go on in a person's head. However, that kind of behavior resembles elitism. Hell, many such people even made memes like "Elitist Linux Asshat" to rub others' noses in it. Starts to get harder to deny their ego and aire of superiority is involved at that point.
See how your centralization point was pushing your ideology instead of apparent claim that Slack was only good due to centralization?
"You know, it's not that open source devs are elitist, but they have a history of writing code for people that are the 10% technically elite. It's not that they're smugly arrogant, but rather, IRC does the job they need it to."
Oh no, he's right. Ask them to change anything to something easier. It took quite a while to get the GUI clients that simplified key steps. They were insistent on forcing people to learn and memorize commands instead of menus with obvious options. They certainly could've improved look-ups and had "save to favorites" earlier in usable form. They didn't care because they were elitist.
Now, I'd consider a different explanation if tech people weren't doing same thing for UNIX commands, GUI configuration, installers, incomprehensible-by-default text editors, everything is a command line argument instead of sane menus of text, and so on. The amount of mental load it took to use those systems and apps vs Windows or Mac is a huge chunk of why they dominate the desktop.
I recall the pain of switching to Linux from Windows. Everything that was simple or easy to find just clicking around took thought in Linux. I knew that was unnecessary because my previous supplier made it unnecessary by putting in work. I later saw Apple do the same for network configuration, backups, and getting apps mostly safely. Elitists are still bragging about their commands, ports, and so on while known UX or foundational issues never get fixed.