If the Zawinul bio is to be believed, the backing, the serious backing, for the band began to really fall into place after they had reached their creative apex. So from a business standpoint, it made sense to keep going as long as possible. Wayne needed the money for his family, and Joe was really into building a business. Reality, that's what I think it could be called.
Those post-Jaco albums aren't at all bad (aside from This Is This, which is every bit the hastily-assembled "contractual obligation" album that it sounds like), and like I said earlier, Domino Theory is one that is too easily overlooked/dismissed. You can even make a killer single album of the best material from those albums. But as far as the real discoveries and adventures, that had already happened. Men with less to lose than Joe & Wayne would probably have packed up & moved on long before they did. But, really, who can blame two middle-aged jazz musicians for wanting to have something resembling a real piece of the pie to show for all their work? I can't.