Women love blank slates, because it provides a way for them to project themselves on them. Twilight was a HUGE franchise in the very late 2000s and early 2010s,
Blank slates (male or female) are deliberately written so that the lizard brain of an audience member can't easily "other" the protagonist. You're supposed to subconsciously put yourself in their situations more easily since being so generic. There is a distinction between the blank slate male and female however, typically the blank slate female wants to "do right" and "get along" whereas the male wants to "just get by" and "not be hassled."
People absolutely hate blank slates as characters though, especially opposite gendered ones. You could take some blank slate male protagonist and show it to a woman and I bet she'd not like him. It's another type of test for people, if someone is an actual fan of a blank slate protagonist like Bella, they're probably a dumb normie who can't relate to anyone not a dumb normie like themselves.
My theory that I've mentioned before is that they believed young men with a mind receptive to nationalistic rhetoric would be put off by it if it were coming from a character who looks like a stereotypical leftist woman, not realising that most men of all political leanings actually love alt chicks, even if some may be loath to admit it.
I think you're giving them way too much credit. Look at any, what we used to call "SJW", media. Everything is written with a combination of official college led story structure/characterization and TV tropes. It lacks originality and introspection outside of the author's personal beliefs/interests and styles.
They don't think "men would be put off by girls who look like stereotypical leftist women" they're thinking "what would a bad girl wear in a contemporary school setting?" They've taken the current fashion they know, start coding aspects of it (short hair, cooler color pallet, choker) as non-properly feminine and call it a day.
They don't think of things in terms of X group stereotypically looks like that or stereotypically men of x group of course wouldn't like the appearance of stereotypical women of y group because they're y group, so let's subvert that.
When the left subverts things, usually it's in the realm of normalization. More "making Amelia trans" not "your edgy based girl dresses like Ramona Flowers". The basic SJW lacks the ability to reflect on these things, they simply apply what they're taught and shown on their reddit boards. That's why they make stuff like High Guardian Spice or Magical Girl Friendship Squad.
