>>106012125
It used to be on the back of the card back in like the HD4870 days (or even sticking out of the PCB on the 4870x2), but GPUs are used for a lot more than gaming now
Power on the top ensures that using these gaming cards in rack cases where there's not a lot of vertical space is difficult and requires either modification or wasting space. Notice how on the fancy workstation and server-grade cards the power is always on the rear.