They needed private IP ranges that wouldn't conflict with the real internet. 192.168 was just sitting there unused, so they grabbed it along with 10.x.x.x and 172.16-31.x.x.
It isn't an article, but a mailing list post, and the post starts out with:
This is a fuzzy recollection of something I believe I read, which might well be inaccurate, and for which I can find no corroboration. I mention it solely because it might spark memories from someone who actually knows:
Spoiler: it sparks one memory from one person, who winds up being mistaken.
Offering an alternative hypothesis seems reasonable given the content of the post.
Modern apps are way more complex than Quake. Dropbox needs threads for syncing files, watching folders, updating UI, etc. Steam's web helper is basically running a mini-browser.
Back in the Quake days, we had single-core CPUs and tiny RAM - every thread mattered. Now with 16+ cores and tons of memory, it's cheaper to just spawn threads for everything rather than write complex single-threaded code.
Your computer's fine - this is just how software works now. We traded elegance for "throw hardware at the problem."