Hi, big brake and racecar dork here. I feel compelled to add to this because I feel like the top answers are missing a degree of complexity in this.

While yes, in general, multi-piston calipers are going to provide more stopping power, it’s not quite as simple as heavier cars = need more brakes, therefore more pistons more brakes! My 3/4 ton pickup is heavier than any passenger car save maybe a model Y or a wagoneer, yet it has simply huge single piston brakes that will happily lock the tires up.

Brake torque is a function of pad mu, piston area, brake diameter, and the pressure generated by the master cylinder. The main advantage of multi-piston brakes is that you can more efficiently utilize the pad area for pistons. This leads to more even pad wear and more piston area for a given caliper size/diameter than you would otherwise manage. They are also much stiffer than single-piston calipers.

So, I have a couple of theories, as it’s hard to know exactly what decisions are being made behind closed doors.

First, for a given brake size and diameter, more piston area does improve the amount of brake torque generated per pedal effort at a given master cylinder size. I acknowledge that this is restating the whole “stops better” idea in a much more convoluted way; however I think part of the motivation is that at some point larger brakes get very heavy and unsprung weight is pretty awful for mileage and performance. Multi-piston brakes let them hit brake torque and feel targets without going with huge brakes.

Second, I think the feel aspect is likely the larger motivation. Like I said, you can spec huge single piston brakes that will absolutely still lock the tires up, but they won’t feel very good, and they’ll need a bunch of pedal effort due to the smaller piston area. Consumers of performance road cars simply don’t know much about what makes good brakes, and so the brakes feeling “grabby” is what they think good brakes feel like. Lots of piston area creates grabby brakes with short pedal travel without a ton of effort - this is the key thing in my estimation. The stiffer calipers also contribute to a stiffer and more confident pedal.

Finally, I really don’t think you should underestimate the appeal of big performance brakes under nice wheels. It’s one of the most obvious signals of a “performance” car, especially luxury cars that want to communicate fast but not overly flashy. That might be my bias, but I think that’s something people absolutely pick up on and it influences their opinion on the appearance.