The modern myth is probably wrong. I've heard Carson wasn't thrilled about giving up the show; it was just the least bad option open to him. (That he wasn't entirely ready to drop tools was evident in his occasional post-retirement feeding of jokes to Letterman.)
Whatever the truth, Carson was beloved because he wore his crown as king of late night lightly. When he played power games, they were low-profile and he didn't drag the audience into them.
Leno has never seemed to accept that he isn't Carson, nor that the late-night landscape has changed drastically since Carson's heyday. Leno seemed to resent being treated the way most entertainers are treated by the bean counters, i.e., shabbily. He wanted to be special, like Carson was (in Leno's mind, anyway).
When Leno felt disrespected, he did not play the good soldier: he needled NBC executives in the monologue and groused about them in interviews. Whether he was right about them was irrelevant. Going after them hurt him, not them, by laying bare his neediness.
It's baffling that nobody in Leno's inner circle seemed to be able to explain this simple truth to him: if you want to be loved, don't look petty. You take the high road and suffer your indignities in silence.
Ah, well ... live and learn, Jay.
Leno might be offered a second (or would it be a third?) shot at late night, maybe by Fox. He would be mistaken to take it, though. If he has any self-respect, he'll make his retirement from that arena stick this time.