Because Shoujo fans tend to shit on Shounen romances as if their precious Shoujo / Josei mangas isn't also full of bullshit tropes and problematic themes that are treated as normal. I love Shoujo / Josei but a lot of readers are turned off because of how batshit insane Shoujo / Josei fans are and how they defend rape / harassment/ coercion as a normalized theme in the demographics.
When I first encountered (American) shoujo/josei fandom, I found people that in fact didn't like those things.
On the other hand, they were obnoxious in their own way-- more than avoiding works with said tropes, they got on their high horses about how they were "problematic". They would consistently whine about how boys/men have little interest in shoujo/josei manga because of misogyny or something, and they owe it to them to finance those demographics because girls freely read shounen/seinen, and shounen/seinen owes so much to shoujo/josei.
Aggressively snobby and entitled sorts, with no empathy for boys and men despite beating the ground for them to financially support markets that are doing just fine.