It's hard to make healthy relationships that are fun to watch on screen (there's a reason TV shows almost always flounder after a "will they or won't they" storyline gets resolved). It's easy to make a bad relationship look exciting and cool, because that's the fantasy -- the partner who gives you permission to break society's oppressive norms.
So it's not that weird that Twilight has a whole subplot about a girl whose werewolf boyfriend permanently disfigured her after losing his temper during an argument. Of course, she still loves him, because he couldn't help it and now he's extremely vigilant about keeping himself under control. You know how guys like that are always able to keep that promise.
This has all been discussed elsewhere, of course, but even in an intentionally edgy story like Fifty Shades Of Grey, the morality police focused more on the consensual BDSM stuff, and not the fact that Christian pulls Anna everywhere like she's a rolling suitcase, isolates her from her friends, and tells her what she can and can't eat. And women love it! It sold 125 million copies.
Because romances have to have dramatic conflict, these dark outbursts are written as the obstacle the pretty people have to overcome, the midnight before the dawn. In real life, these arcs repeat themselves over and over -- lashing out, profuse apology, peace, lashing out again -- until it reveals itself to be a cycle that the victim can't escape.
Related: Why Movies Teach Men Horrible Lessons About Sex
They Can See Aggressive Men As A Shield
A 2016 study found that women who perceive themselves to be at greater risk of victimization tend to prefer physically formidable and dominant men. This is regardless of whether they actually are at a higher risk of victimization -- it's only their perception that matters. Well, let me tell you that no one on Earth feels more at risk than a teenage girl.
Little girls are beloved by society, while teenage girls are reviled. We hate the way they talk and dress. We mock the music they listen to, the TV shows and movies they watch, the books they read. When the backlash to Twilight occurred when it first came out, it wasn't driven by people calling it problematic; it was the world turning up their noses at these shrieking girls in their Team Edward shirts. Teenage girls are trendsetters, and every new fad is met with derision.
From a girl's perspective, overnight, grown men start flinching when you approach them, like there's a sign on your forehead that says "DANGER: DO NOT ENGAGE UNTIL OVER 18." Or even worse, men who've ignored you your entire life are suddenly way too interested, in a way that makes you super uncomfortable.
The idea of having a homicidal boyfriend to put between yourself and the rest of the world doesn't sound like such a bad idea. Especially because a lot of those guys who are way too interested in you won't respect you as a person, but will totally respect you as the property of another man. See, because then grabbing your ass would be like denting that scary dude's car, and he doesn't want any trouble. At the time, whatever leaves you unmolested sounds like a good deal, even if that big aggressive dude you're dating occasionally turns that aggression on you.