Sounds to me like they don't make strict rules for you because they don't need to. You're not overly impulsive, you manage your time and basic needs (like sleep) in a sensible way, and you're doing well academically. Why should your parents come down on you with a bunch of rules and restrictions when they don't really have to? Chances are they've had trust on your maturity and common sense since you were quite young, and now that you're older feel comfortable extending more freedom to you than parents of other kids your age.
Honestly, I grew up an only child and my parents were much the same (I had a *few* more rules, but cell phones also weren't ubiquitous then so it was more important for them to know exactly where I was), and now raising my own kids, my son is turning out to be a kid like you. He's always had good impulse control, he's patient (usually), he's good about getting enough to eat and enough sleep and communicating his feelings and needs. I imagine when he's older he'll probably be allowed a longer leash than some of his peers, which I'll be happy to give him as long as he doesn't abuse it.