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Originally Posted by VIERsr

As far as I know, Bmw does not manufacture or design brakes.
They merely choose which products to use from those offered by suppliers on the market (Brembo, in this case).
Brembo (not Bmw) produces both more expensive and higher performance solutions (multi-piston rear calipers with e-brake integrated) for exotic supercars, and simpler and cheaper solutions for street cars (floating single pot caliper with e-brake).
They could have chosen the more expensive solution and I'm pretty sure Brembo would have been more than happy to sell them, but it probably wouldn't have been worth it considering the intended use, that's all.

Exactly. Thus, more profits.