If the author favors decentralization, then they should advocate for decentralization of the economy, not decentralization of just the Internet. Unless they imagine some utopia where corporations no longer get involved with the running of the Internet, then one has to consider how other economic factors, and also the law, contributes to corporate centralization, which in turn leads to centralization on the Internet.
There was a stretch in the mid 20th Century when most Western economies saw a limited amount of geographic decentralization, as industry left the cities and moved to the country-side. The USA was the leader of this trend. But since the 1980s there have been forces working, throughout the economy, to re-centralize various industries. We see this most dramatically in the tech industry, especially in the USA, where the number of computer programming jobs has plummeted in areas such as Ohio, Illinois, Arkansas, Kansas, etc, while rising in California and New York -- the programming jobs were once distributed across the country but are now increasingly concentrated into 2 mega-urban zones on the coast.
Urban centralization tends to be influenced by political centralization. If the political system concentrates, then the urban system will tend to concentrate. Consider: "Empirical studies of [urban] “primacy” identify two strong factors determining the size of the largest city: urban population as a whole (no surprise) and, more interestingly, political structure: federal or decentralized systems do not have primate cities as large as those with high centralization. Thus Mexico City is still larger than Shanghai, because of China’s
decentralization."
http://siteresources.worldbank.org/DEC/Resources/84797-12518...
Political concentration increases the economies of agglomeration: "The term economies of agglomeration is used in urban economics to describe the benefits that firms obtain by locating near each other ('agglomerating'). This concept relates to the idea of economies of scale and network effects. Simply put, as more firms in related fields of business cluster together, their costs of production may decline significantly (firms have competing multiple suppliers, greater specialization and division of labor result). Even when competing firms in the same sector cluster, there may be advantages because the cluster attracts more suppliers and customers than a single firm could achieve alone. Cities form and grow to exploit economies of agglomeration."
http://en.wikipedia.org/wiki/Economies_of_agglomeration
Furthermore, there has been a decline in the number of startups (which therefore concentrates more power in the hands of older firms):
https://www.fedinprint.org/items/fednsr/707.html
More so, the law encourages corporate leaders (of firms listed on stock exchanges) to focus on hitting quarterly targets. Any significant deviation from earnings expectations is now sufficient basis for a lawsuit: the CEO has mislead investors, this is a breech of fiduciary duty, what about shareholder rights, etc, etc, on and on, I'm sure you know the rhetoric. This tends to mean that firms can only grow to a certain size before they get bought by an older firm, as going through with a public listing is more demanding than it used to be, and exposes the firm to more legal risks than it used to.
We should not expect that the Internet to escape the wider forces at work. If economics, and the political system, encourage centralization, then we will see centralization of the Internet.
You either advocate for decentralization of the whole economy, or you don't advocate for decentralization at all. The Internet is not free of the economy.
All that said, it is worth remembering that there has been dramatic decentralization of industry over the last 70 years. In 1945 the USA accounted for 50% of all global industrial production. Nowadays, it accounts for less than 20%. Asia has seen a dramatic rise in its share of industrial production.