The reason the brakes are designed such that 60% of the braking is nearly carried out on the front wheels is because the majority of the mass is behind the front brake. Car's foot pedal breaking system is set up to send a majority of the breaking power to the front breaks.
When your driving next time, slam on your brakes. You see how you and everything flies forward. The weight of the car goes toward the only things actually touching the road, the tires. The front gets the most weight. That's why it needs the bigger pads.
put it this way, if all/most of the braking were at the rear and you were to "slam" on the brakes you would spin out (like if you put on the e-break/hand brake). so they put most of the braking force up front and only some in the back, so you dont spin out