My Mom is frustrating me?

ok so I'm 17 male, and I've always wanted to bu my GTA V, and I can, I have my own money, but my mom doesn't want it in the house, I have 5 younger siblings, and I've promised her that I won't play it around them, but all she says is she doesn't want it around. She's fine with me playing video games like that, but she won't tell me why I can't get it, I'm guessing it's because of my siblings. I've kept promising that I'll keep it away from them, they're hardly ever around me anyways. I'm just annoyed cause I've always been an angel child, I don't drink, smoke, have sex, and do drugs. I'm mature, I don't freakout, I get straight A's in school, and got a college scholarship, but yet she doesn't trust me to with one video game?