Because while it exists for both primary and secondary sexually dimorphic characteristics, it is much stronger for the secondary ones.
That is actually not uncommon—I can only offer anecdata here as I’m not aware of any studies on the matter, but have met rather a lot of trans and genderqueer people who find secondary dimorphic characteristics to be much more emotionally-salient to dysphoria than the state of their genitalia. It also not infrequently shifts over time—some people seem to change on that after being hormones for a while, or after getting some major procedures (not necessarily GRS) done. I know a post-op trans woman who still gets very strong dysphoria because the secondary characteristics still feel wrong to her.
That is actually not uncommon—I can only offer anecdata here as I’m not aware of any studies on the matter, but have met rather a lot of trans and genderqueer people who find secondary dimorphic characteristics to be much more emotionally-salient to dysphoria than the state of their genitalia. It also not infrequently shifts over time—some people seem to change on that after being hormones for a while, or after getting some major procedures (not necessarily GRS) done. I know a post-op trans woman who still gets very strong dysphoria because the secondary characteristics still feel wrong to her.