because Supra owners spend the money. The aftermarket doesn't pick names of cars our of a hat and say ok we will make parts for this car now. If there is a demand then they will push to make better parts. It's business plain and simple. Why would Greddy or HKS invest time and money into developing a product if there aren't a lot of people willing to spend the money to buy the product. It's the same reason there is such a strong aftermarket for Hondas. They don't make parts for a Honda because it's such a strong platform to start from. They make parts because there is an ass load of rice boys willing to throw stupid amounts of money into their civics and integras.