I think it’s not that people with prodigious abilities don’t want to attribute that to their success so much as mentioning that as a factor comes across as very narcissistic and unlikeable (even if it’s true) unless you are literally an Einstein/Von Neumann type. For example, even Terry Tao has enough humility to self censor himself not to attribute his success to being a far-outlier-genius.
In fact I’d bet a lot more people think to themselves that they are only successful because they are a genius than there are geniuses. Because it’s even more likely that coming from a highly rich or well connected family is truly the key factor in their success, and people would would much rather attribute success to talent or intelligence than daddy.
It is definitely true though that prodigious talent isn’t by itself sufficient to be successful. Also, intelligence helping you is kind of a given - it’d be like an NBA player saying “being 6’8” really helps”. There are a lot of really tall people not in the NBA and a lot of prodigiously talented people who aren’t conventionally “successful” either.