Because everybody assumes "dark, gritty, and edgy automatically equals good".
It's a game for crying out loud. Loosen up, have some fun.
For some people, a CG showing two Abyssal girls, one held in the other's arms, is a tragic image that makes them question what makes an Abyssal different from their shipgirls and automatically assign a backstory to it as if it was the most important day in their lives.
But for others (like Gomasamune here), it was just Friday's boss run.