Why Rears worn out before the fronts?

Take a look of the OE brake set up can help you better understand why OE rear is insufficient which does'nt get bigger along with the front rotor size (horsepower) over the versions:

Rotor size: Front/Rear (mm)
WK1: 360x32/350x28
WK2: 380x34/350x28
Trackhawk: 400x36/350x28

Brake caliper & pad
WK1: 4 pot/4 pot, PD1149/PD592
WK2: 6 pot/4 pot, PD1291/PD592
Trackhawk: 6 pot/4 pot, PD1395/PD592

We highly recommend rear BBK (390x30) for a balanced brake for Trackhawk