For many teenagers, getting their first car is as big a rite of passage as going to prom, working their first job, or having their first kiss. It signifies an extra level of freedom from being dependent on their parents, and it gives them something to show off in the high school parking lot.
By the same token, the first vehicle that they own is unlikely to be the flashiest one that they'll ever have. It's unlikely that anybody who has barely got their license can afford their dream car, and if somebody else is paying for it they probably aren't going to want to make that investment.
This is an issue that caused controversy on Twitter recently after texts were shared between a mom and her teenage daughter who had been gifted her first car. She said that she didn't want it as it was 'not [her] style', and the audience was divided about whether she was in the wrong or not. It could definitely be seen as ungrateful, but it's also important to drive a car that you enjoy.