It's due to the fact all the panels in the front are aluminium, and there's bugger all metal in front of the firewall excluding the motor.
The engines are mounted far back in the engine bay and the gearbox is between the front seats pretty much.
The rear body has a shitload of steel in it, along with a heavy subframe, and they have a big rear overhang compared to the front.
Rear hatch is also damn heavy, with the bonnet weighing next to nothing.