(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.
Their core is apparently based on Mer which was a reconstruction of Meego, which was what came after Maemo, merging it with Moblin, IIRC.
It's a bit tenuous, but you might want to look at Sailfish as carrying the torch in that area.