No one knows. It could have been a business decision or a technical decision.
The magazine advertisement is dated 1965 so you have to look at the context of
other projects he was involved with at the time. You can look at Wikipedia and
see his other models ..... if anyone here is familiar with editing the Wiki articles please let me know and we can add the SuperDemosielle info and pictures. A google search for the SuperDemoiselle now turns up the info contained in this forum thread.
From the photos I have, I see an original prototype made from welded steel tubing
that was redone in bolted together alum tubing.
I agree...it had an ample of power and seem that the fairing around the pilot was very different in each iteration.
He had started to design BD-5 already in 1965....maybe he did not want to produce many planes at the same time ?