How is having a large chunk of the internet using the same CDN provider not "centralizing"? It's not a hard monopoly obviously but still it meets the definition of centralization.

how is private companies choosing to use a common supplier in a competitive market centralization? monopolies are not centralization either. you need to read a better book.

How is a market competitive when there's a quasi-monopoly on infrastructure? When public money is used to irrigate the same corporations with huge $$$, while non-profit network operators are left to rot?

it's centralization because they all use the same provider. Why do you care about incentives here? The result is the same, just like capitalism and free market tend to monopolies in the long run.