To be any good ABox had to be finished first, and be of high quality. That took a very long time.
QBox, (or rather several different OSes running at the same time which was the bigger plan, something like highly efficient vmware) would have required major overhaul for drivers and such (you wouldn't have been able to run them inside ABox obviously). Basically it would have required way more resources than were available. The commercial (as in making a living just coding this stuff) side of things pretty much dying didn't help either.
So, rather than taking the very very hard route we instead chose to expand the ABox side. Yes, it doesn't allow some of the wildest dreams of the QBox thing, but it still is very good.
Am I in any way disappointed in all this? Not really. Even with "just" ABox, MorphOS still kicks serious behind and is great fun.
