Less desirable and low value cars are cheaper to insure
When I was 17 I wanted to own a Ferrari and live life in the fast lane. Even if I could have afforded the car, then I couldn't have afforded the insurance to cover it. At 17 you are brand new to the world of driving and statistically you are more likely to make an insurance claim. Mixing high-powered cars with inexperienced drivers is not something car insurance companies are super-keen about, the chance of a claim shoots through the roof with the price of the premium following