Perhaps because Vowerks -- according to the ABA 2014 standard ---are considered "extinct" as no one has shown them in over 10 years so development would be slow. There was lots of interest in the Vowerk on the APA list and Mike mentioned John Blehm, but honestly he is the only one out there with them -- so I think sourcing at least the Vowerks would be an issue. As for the Lakenvelders, I barely see them at the shows and most are not of good quality. I have one, that I got from John, the others all died, and they are very flighty being based on Leghorns, but the real problem with is the health issue there.
There is an interesting thread on the APA Official site today about how long it takes to develop a strain which is why projects colours come and go -- they do not pick up traction and the one person working on them gets ill, dies, doesn't want others to get the "glory" or just (typically the issue) tired of all the work particularly when Breed Clubs are not very accepting of new varieties.
I think, on that thread, the way to avoid that, is tyler Danke's suggestion is to allow all breeds all colours automatically and then just deal with vetting of them at the shows. Brian Decker, an ABA APA Judge did not like that idea, and I think he is representative of the APA standards committee that wants to control what and what they do not allow -- for whatever reason. I believe that needs to change.
Sue