People do. There are a few locally tracked/raced cars that are 100% stock and are exceptionally reliable. Also lots of people just driving 335/535 as commuters, you just don’t hear from them.

Brakes turn kinetic energy into heat, the rotor then dissipates that heat. Multiple pistons dont necessarily improve the braking performance. My thought on this was because of the weight and because aluminum is less energy intensive to cast (cheaper). A lot of dampers are also aluminum now, and so are uprights, so mass has for sure been a large factor in the decision making process for most car manufacturers.