Recreating the original design has resulted in a well thought plan for Glass Elevator and there is significant interest in getting Phase 1 done so the fun can really start.

If this is such a great plan then why have others gone their own way?

There are 4 or so versions of BeOS growing in the wilds plus Zeta -- Blue eyed OS, Cosmoe, Sequel and Befree. These are all works inspired by BeOS but going in a slightly different direction than OpenBeOS. All these development efforts help build a deeper understanding and experience of the basic architecture.