You might not be able to afford to put up power lines or build a road, but that doesn't mean you physically cannot. By your logic there are no natural monopolies
If I want to service 1234 sesame st from my physical location with power lines there are a very limited number of routes I can take. The limited physical space quickly becomes crowded, duplicate physical infrastructure of that nature is highly inefficient, and there's a (completely pointless) negative impact on society to accommodate the constant installation and servicing.
Commodity hardware installed in a commodity building on commodity land using commodity power hooked up to a commodity network isn't the same thing. By your logic anything expensive or inconvenient is a natural monopoly. I believe the term you were looking for was "high barrier to entry".
