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.