Even as a guy, I don't like fat. I would say it's a "way of life". Nothing pretentious, just that sport is part of my life (NOT my life, I'm not living in the gym lol). You're right though, it's stupid to not find someone attractive anymore just because he/she gained weight when you know the person (and it's not helpful for the person, it's the opposite).
I admit on some girls, having some fat make them attractive, like Kawane Kurumi (like an adult baby, if it makes sense).
Yep, it's her job to look sexy. And she's a S1 girl, only one movie per month, she has more time compared to freelancer to stay in shape. She doesn't even have to go to the gym (even if some actresses do it, kudos to them) just eat healthy food. You can have fun and eat a cheat meal once a week, but not everyday.