[dragonwriter]

That assumes it is acceptable to talk about it equally across genders.

But it's not exactly implausible that people socially gendered as boys face stronger social pressure against revealing insecurities, in general, both in their peer groups and in general.

Even with no difference specific to gender dysphoria, this could prevent the same phenomenon from manifesting with boys, or at least create a higher threshold of societal awareness and acceptance of gender dysphoria before that acceptance combined with the degree of general acceptability of boys revealing insecurities produces a similar effect to what has been seen in girls in this case.