Gojo is a talented tailor, has a hobby that perfectly jives with Marin's, is conventionally attractive, and is 6'1 (as a Japanese teenager).
Only reason he's not already popular with girls is because the (female) author needs him to be an outcast for the sake of the story.
Yup. Boom.
I finished both Nagatoro and My Dress-Up Darling. In no way would boys like Hachiouji and Gojo land girlfriends like Nagatoro and Marin. In no way would girls like Nagatoro and Marin be nice to boys like Hachiouji and Gojo.
It's fiction. That's the point of it.