If it was up to him alone, would ST be as near-and-dear to his heart as "The Lieutenant"? Or just another project he worked on decades ago?
Granted that he left the show in S3 because he wasn't getting his way and he was pretty much replaced.... It shows that he didn't really care much for ST at the time to continue fighting for it... or he considered it not worth the headache. Or maybe, perhaps, he saw the show dying and decided to focus on new endeavors.
Whatever the case maybe, he was quick to jump back on that wagon train to the stars when it started becoming lucrative.