For reasons of economics, they need to be able to share parts with other models so they can't deviate too much in terms of design. When regular car companies do

For reasons of economics, they need to be able to share parts with other models so they can't deviate too much in terms of design. When regular car companies do build unique sports cars (e.g. Nissan GTR, Lexus LFA, Ford GT, Acura NSX), they end up being more expensive anyway, so they would have to put in the performance to match to justify the cost. Even swapping in a cheaper drive train wouldn't make the car dramatically cheaper.