Earlier quoted context omitted.
ISPs is an anecdote, economies of scale in most business means products are much cheaper if provided by large companies, so where is the cutoff between "monopolies" and simple economies of scale? The author claims 6 seed companies are worse than hundreds of seed companies, but doesn't give a single fact to support that claim.
You bring up an important point. I have thought about this issue a lot. For ISPs the problem is that companies tend to expand. So where 20 years ago an ISP might have been a small regional provider. Things have consolidated and expanded so now that same company owns almost the entire infrastructure and many other services that depend on it. They can also bundle services together to make it harder for a new competitor…
Not cooperatives. Co-ops tend to focus on their region, and have neither a reason to push into other territories, nor usually the foothold to do so as easily as in their own region.
"Farming out" your lines to outsiders then deciding that you don't want further construction efforts because 'the cables are already there' - effectively giving them a monopoly over your region - is what got us into this mess in the first place.