I think it's because they're not open source. Most of them anyway.
So a couple of minor road bumps and tada the project disappears forever.
Natami was actually really promising hardware and software, it's a real shame it's gone under. Even just the n68050 would have been promising to have been open sourced, then things like the Vampire 600 might have been designed differently to accommodate it, instead it's vanished into the Apollo project and is still closed :/
If you're going to start one of these things, start it on GitHub, put _everything_ on there, give it a BSD/GPL3 license or something.