Well it sounds like an instance of "your keys are always in the last place you look, because then you stop looking"
Before the match, the expectation was that Gukesh would take an early lead and never look back, with the match ending before game 14. This morning, the expectation would be that Ding would make an easy draw with white (as he has done in 5 of his games as white already, winning the other), and it would go to tiebreaks.
Having the championship decided by a decisive final classical game is pretty rare. The last time it happened was 2010.