Breaking G is also more or less required for the drivers to break properly.

All breaking force has to be generated by the driver as per regulations, and the pedal requires over 100kg for maximum breaking, all while modulating the force precisely to extract the maximum without locking up[1].

So they rely on the breaking G forces making their legs heavy.

[1]: https://motorsport.tech/formula-1/formula-one-brakes-explain...