The context here is the technology available at the time of the introduction of FM in the mid-1930s. In that context, schemes for reduplicating AM over a much wider bandwidth than the ~40 kHz needed for high-fidelity audio may be interesting in their own right, but they have no bearing on the article we are discussing. AM, as it was construed and implemented at the time, was inherently limited to a bandwidth just twice the signal frequency.