Decentralization is a way of removing dependencies and adding redundancy. It's often less efficient, there's way more duplication of effort, but can be more resilient.
Big players don't necessarily have an interest in this, but some do. It's always a balancing act between too much centralization (single target/point of failure) and too much decentralization (impossible to control).
I'm trying to think of specific actors that have interests in this, but I'm finding it hard. Not the NSA, right?
I don't understand why you think decentralization is a balancing act. What do you mean by "impossible to control", and why would that be bad? What would "full" decentralization even entail? A network of sentient computers doing whatever they want, except using supernodes "too much"?
(My definition of supernodes: nodes that transfer significantly more traffic than others structurally, in practice nodes that accept incoming connections, like servers or BitTorrent supernodes, but also AS's.)
The military and certain branches of the government (e.g. CIA) are very interested in having modular, autonomous structures that can survive in the event of a decapitation attack, or if communications are severely disrupted through other means.
They're also interested in having centralized control so the various components of their organization are not running rampant and in conflict with the others.
It's a delicate balancing act. Look at the US as a whole: If states are too independent they might get into wars with the others, not unlike The Holy Roman Empire. If they're too much under the thumb of the Federal government they'll feel oppressed.
If (my example) instead of people messaging each other on facebook, every single person needed to run a server (such as an IRC server) at home - no centralization at all. (If five people want to talk to each other, there are a total of 10 connections because 4+3+2+1 to fully connect every node with every other node). That would be an (extreme) example of decentralization, and obviously centralizing chat so I can just use a thin facebook/whatever app is hugely convenient. Likewise the blockchain is a joke, a single $200 pc can trivially do the work of the entire bitcoin network, trivially - if it were centralized. This second example also shows what is meant by control.
So it's a balancing act.
The internet is both centralized, we need to agree on protocols, coordinate address spaces, issue domain names, and decentralized, where elements of it can survive independent of the others if they're temporarily disconnected.
The Bitcoin blockchain is an example of something that's a complete contradiction: It's a highly distributed highly centralized system. There's only one Bitcoin block chain, and everything must be recorded there for it to be valid. If, for example, Iran is cut off from the greater internet then that means you can't use Bitcoin in Iran.
BitTorrent is a much better example: There's no central authority, it's truly distributed, and highly fault tolerant. If Iran was cut off for some reason, all the Iran-hosted seeds of any content would still work.
Big players don't necessarily have an interest in this, but some do. It's always a balancing act between too much centralization (single target/point of failure) and too much decentralization (impossible to control).