Hi Tourist,
I will possibly accept that something usefully aerodynamic is starting to happen IAS >50kts, but that is also the case with a tailwind, obviously, so why the difference in procedures.
By increasing the load on the nose wheel, you improve the nose steering capability with rudder bar deflection. Initially up to say 50kts, your ground speed is low and there is time to react before you run off the side of the runway after an engine failure. As you approach VMCG, the rudders will have sufficient control hence relax on the nose down bit.
With a tailwind, you'll need more even more elevator to provide the same nose wheel steering for the same ground speed.