The whole idea behind that was that (within reason) the more N you can pump into the crop, the more it will yield. Wheat is essentially an inverted pendulum when ripe, with about 60% of the above-ground biomass perched at the top.

The main thrust of modern crop breeding has been to create crops that you can successfully get to harvest under high-nutrition environments, without it literally falling over or succumbing to disease due to the turgid, fleshy growth. Even then, if you're applying more than maybe 150kgN/ha, you will be relying on plant growth regulators that inhibit auxin/gibberellin response to keep the plant under control.