Many observers overplay the importance of one match loss. More than one chess champion title was taken by a challenger who had lost in the previous attempt [1] - and considering there was just a handful of champions, it is a lot.
[1]: Spassky and Kasparov have lost in their first attempts against Petrosyan and Karpov.
Magnus specifically mentioned Firouzja as an opponent that he would consider playing the WCC against[1]. So while not the most important factor in his decision, the fact that Nepo won the candidates again and was the last challenger before Magnus made the Firouzja statement seems relevant. Also relevant is that the candidates tournament concluded on July 5th and Magnus released his withdrawal now in the same month.
It seems to me like the challenger being Nepo was the last significant piece of information towards his decision. How specific it is to Nepo or a more general feeling of Nepo being one of many people he doesnt feel any personal benefit from playing against, who knows.
[1] https://chess24.com/en/read/news/magnus-carlsen-unlikely-i-w...
That is not how it works, and not how it is supposed to work. This is hubris and disrespect to all chess players in the world. For more than 100 years champions changed each other in title matches (well, before Kasparov's limitless ego created a decade of turmoil in Chess), with just one exception by Fischer, and now Carlsen 'doesnt feel any personal benefit'. :ThumbDown:
So it isnt the most important reason, but nepo being the challenger didnt offer anything to change his mind like he was hoping the result of the candidates would.