Firstly: Designing an appealing sports/luxury car is expensive and many companies hire skilled professionals from known design firms to help accomplish this. The design often comes first and much of the car is constructed to fit the aesthetic and theme. Cheaper vehicles are more utilitarian with a more “that’ll do” attitude instead of being designed with artistic intention.

Secondly: Almost ever car maker has their own luxury brand or subsidiary. Selling cheap luxury/sports cars would undermine their own brand’s prestige and market segregation. There is a reason why dedicated luxury brands will not make budget-friendly vehicles unless legally forced to.