Why must John le Carre keep tinkering with George Smiley?

New book seems like attempt to recalibrate events in earlier work

In what way does George Smiley, the squat, diffident serial cuckold with a lifetime's devotion to the Intelligence Services, resemble John le Carre, the dashing, rangy, sometime ladies' man who said goodbye to the Circus 50 years ago in favour of living by his pen?

I would suggest the answer is that they are both craftsmen. I imagine Smiley in his old age looking back at the operations he devised with the same appraising eye that his creator might cast over his couple of shelvesful of novels. Both men might wince at some of their wrong turns, but they would also take justified pride in the dovetailing of their ingenious plots with their unusually acute understanding of human nature.