That could be it. Maybe writers don’t want to tamper with the great work of other writers. That’s what makes Jenkins retcon even more unnecessary, he basically retconned a seminal run for no real reason or pay-off.
Interestingly, I think the most recent sightings of Professor Hulk are in the Maestro minis that PAD is writing.
Or at least I think that’s Professor Hulk that becomes the Maestro. Duggan seemed to be suggesting it was Doc Green that becomes the Maestro eventually so I’m not sure how everything fits into cannon.