The thing with fiber is that it can go so much longer than copper without any active components. It is also very future proof, you won't be pulling it out of the ground/off the pole for at least 50 years if not longer.
If size is such an issue, how did you get power?
You're not conflating 2 different infrastructure processes and ignoring the one took decades, are you? This is like saying "The US has built a road infrastructure why can't it do all light rails?"
The irony in your comment is that it government intervention, which is the opposite of a free market.
You can't have 2 road networks, highway systems, or railway networks. You can have, but it is pointless to, 2 water systems or 2 electric grids. Or fire brigades, or police. (criminal, not mall cops) Same applies for fibre in the ground. "Free market" doesn't work when you can't effectively compete.