Howard, W3CQH wrote:
"So then, what is the reason they drive a separate ground rod in when
they install a commercial tower whose legs are in concrete?"

Working with electricity you soon learn you need a rubber mat or rubber
soled shoes to protect against electric shock from the mains when you
are on bare concrete. It is often damp directly on the earth. When
poured as a slab, concrete is placed on plastic as a vapor barrier to
keep wood flooring from warping.

A tower base after years is not completely set but still contains
moisture and is still hardening.

Tower bases are bypassed by ground cables outside the concrete block so
that the moisture inside does not turn to steam during a lightning
strike and blow the concrete asunder.

Best regards, Richard Harrison, KB5WZI