Why is Ethernet So Power Hungry?
Most of the current is the quiescent current of the transmit driver. If you read the datasheet, it explains that the output driver is sinking current through both sides of the transmit transformer's primary all the time. The two 49.9&Omega; termination resistors account for 66 mA of that all by themselves.

When active, the transmit driver must launch a significant amount of energy down the cable, which accounts for the additional power required.

The receive side of the PHY draws a not-insignificant amount of current, too, particularly in the initial analog stages. With all of the constraints on it in terms of gain and bandwidth, minimizing its current consumption is not a high priority.