#1 reason is MOAR Power. Now common midsize sedans are in the 300hp neighborhood. Add to that improvements in wheels/tires and the absolutely vast improvements in auto and computer controlled manual transmissions, and you have a recipe for vast improvements.
Not to say that it's all that difficult to take an old car and get similar results. Take that NSX, put some good rubber on new wide 18" wheels, give it a turbo to boost it up to modern power standards, and you'll probably see basically identical performance to a new car with the same power/weight. Hell, even do some cheap mods to an old Fox 5.0, slap some big sticky tires on the back, and watch the 1/4 fall quickly.
Working with aluminum is still expensive, but was even more so back then, that's a lot of the reason the NSX was so pricey. They could have brought out a similar product with more conventional materials and been a lot cheaper, but it would have been a bit heavier, and most of the point of the NSX at the time was as a halo vehicle/engineering validation.