We never really learned.
What seems clear is that Secret Avengers was forced to wrap earlier than it would, or maybe the three issues in space fucked Remender's scheduling up. I also seem to remember that Pym was at one point one of his candidates to the Unity Squad before he had to rework his plans. My guess is that Remnder wanted the descendents' plot remains to carry over in UA and either editors convinced him to leave it dangling because Waid had other plans for Pym (which eventually were downgraded to Humphries' Avengers AI) or he himself realized that plot would be too large and off-point and wrapped it up here as he could, only to rework the original ideas into Rage of Ultron.
The fact that Pym never appeared nor was mentioned once after this before the Avengers AI prologue makes me believe it's the former, also includind that at one point Marvel REALLY didn't know where to fit the Pym-featuring Age of Ultron event because Bendis and Hitch lost track themselves.