It's the same "illusory superiority" cognitive bias as the Dunning-Kruger effect. The least competent will overestimate their self-control, and the most competent will underestimate it.
I'd go for more of a Freudian "people who are somewhat obsessed with self control (therefore mindful of it) are people who struggle with it," coupled with salience bias. People who don't struggle with self control never think about it.
