I believe it has something to do with how active the account is?
Side note, if the paint scheme request gets rejected, don't give your hopes up! Trust me, once you figure out the controls of your preferred paint program, things go uphill from there. Sure, your first shots at painting the car will not be stunning at first. Like everything, you'll be needing practice. Learn from mistakes. Don't give up. Eventually, when the car is finished, you'll be proud of your work on it.