The idea doesn't quite originate with Krutch, though he was fond of it. His own inspiration is described in the prologue to his book The Forgotten Peninsula, on Baja California, here (as linked in TFA):

<https://archive.org/details/forgottenpeninsu00krut/page/14/m...>

I'd had my own independent awareness of the concept some decades ago on re-visiting an off-the-beaten-path camping spot and discovering that the previously single-track dirt road was now a (still narrow, but arguably dual-carriageway) paved one. This apparently had some positive ecological benefits (far less road dust in local creeks, harmful to fish), but also negative ones: the site was far more crowded, and the calibre of visitors different.

Stumbling across Krutch's earlier formulation was a delight and validation.