The internet will not stop being decentralized just because there are some consumer product monopolies.

When Amazon starts running its own dark fiber, and you can only use that fiber to buy shoes that are only sold on Amazon, then part of the internet will be close to being centralized. But that would still just be a small part of it, and it still won't happen entirely.

There's a very long tail between Amazon and the user. How does Amazon connect to the user? Sure, it starts in their datacenter. But then immediately they need to connect to multiple points of presence, which means multiple bundles of fiber going in different directions. And so you'd say, sure, Amazon has lots of DCs, so they could just run dark fiber between all of them. But they're not _everywhere_, so they need to eventually peer to a more global network.

Eventually you get to the ISP. There's two kinds of ISPs: wired and wireless. While they're increasingly the same company, there is a wealth of technology, expense, competition, and physical infrastructure wrapped up in each. Copper and fiber runs to every home, customer support, billing, management, contracts with public and private entities. There's multiple companies in these industries that are bigger than Amazon.

Say Amazon becomes its own ISP. They can either run fiber to every home (lol) or become their own nationwide wireless ILEC (lol) or they can become an MVNO and rent access to an ISP's gear (possible) or they can just pay internet backbones to peer with them and get access to all ISPs' customers. The first two would basically be like making a brand new Comcast; uh, good luck with that. The third is what Comcast already does: they rent ILEC's networks to provide their own mobile service, capturing more customers. The last is how the internet operates today: the ISP deals with the complexity of getting everyone in the country online, and Amazon just pays to connect to POPs.

In a non-net-neutrality world, any ISP can add a line-item to your bill for you to get access to Amazon. In that case, Amazon becoming an ISP avoids that, capturing more profit in the process. But why in "Bob"'s name go through all that work, when you can just charge people individually to access your website? Aka, Amazon Prime. So in order to completely control your access to shoes, they can either build an ISP, or just..... use existing ISPs. Currently, most ISPs aren't adding line-items to access Amazon, so the latter works fine.

In another bizzaro possibility, Amazon could merge with every ISP in America, creating a hyperconglomerate, so only Americans could access Amazon, and every ISP bill is charged for Prime, and every non-American ISP has to pay to route traffic to Amazon. I think that would just crush Amazon's sales, but it's possible. But still the internet would be decentralized, at least globally.

And one final option that actually already exists in developing nations: Amazon and a handful of other monopolies subsidize ISPs to create a "bare-bones" internet plan, where you literally can only surf to Facebook, Amazon, and Google, but you only pay $10 a month. This would be a consumer-only internet that is totally centralized and monopolized - but it's still not the whole internet.

Then of course there's every other business in the world that is not consumer-oriented, all of whom depend on the internet for their business. They also have an interest in a decentralized internet, because it helps them compete with each other, too. They'd be happy to fund a decentralized internet, if only for themselves.

This is all besides the fact that decentralization is actually an architectural decision made by a central organization - the DoD. They made it decentralized because it just works better, not because they wanted the whole world to hold hands and sing kumbaya. Even in this fantasy world of a centralized internet, with one company managing all the consumer services, b2b services, and internet connections, they'd still keep a decentralized architecture, because they know it's really friggin' robust. The network architecture has nothing to do with who has control.

If your concern is monopolies, an internet protocol does not change this at all. If your concern is being able to host your own services, that's still at the discretion of your ISP.