In one of my Linux handheld attempts, I looked to evaluate Maemo for the vintage Nokia N810 and N900 as a starting point, but much of open source artifacts (code, docs, forums) had mostly disappeared, even from where there seemed an effort to preserve/migrate.
(But someone's copy of some of it might have resurfaced now; I haven't looked recently.)
Usually things like this disappear because whoever was paying for hosting for them (company, accounting unit within a company, or some random techie's basement) gets shut down. And maybe no one who had the interest and ability was able to preserve it in time, and archive.org hadn't picked it up. But occasionally, things get deleted with intention to suppress them.
(But someone's copy of some of it might have resurfaced now; I haven't looked recently.)
Usually things like this disappear because whoever was paying for hosting for them (company, accounting unit within a company, or some random techie's basement) gets shut down. And maybe no one who had the interest and ability was able to preserve it in time, and archive.org hadn't picked it up. But occasionally, things get deleted with intention to suppress them.