Firefox OS uses the same code base as desktop Firefox, so they don't have to hire all new developers to work on a project that won't integrate with their main product at all. Just makes absolutely no sense for them to adopt WebOS. WebOS never had the same goals as Firefox OS, for one, their goal was simply to use a platform that many devs are already familiar with and using, as a way to gain adoption. It didn't work; turns out devs go where the users are, not where their skills are.
WebOS didn't fail due to its web roots; it failed due to lackluster hardware, being late to market, and an untimely power shift at HP. Users not caring about the underlying technology cuts both ways; with better marketing and a couple more years of iteration, it could have become a real contender.
