I don't understand why Lucas and Spielberg would not allow other writers and directors to get involved.

Its the same story as Star Wars pretty much the need to control every aspect of the production.

Its not like a failed tv series like Young Indy where you can allow collaboration.

I think there would have been a lot more indiana jones pictures and more star wars pictures if Lucas path had taken a different turn. No divorce no burnout.

If he stayed young forever, none of those were likely.