Companies, individuals, the government and all can own billions upon billions of dollars in bitcoin, they can own the majority of the supply of bitcoin with which they can decide which direction the price of Bitcoin will go, this is market manipulation, but they can never be able to centralized bitcoin so long as they cant and do not have access to control what happens in the bitcoin blockchain.

We all have to know that the blockchain is the engine house that powers bitcoin, it is the foundation of bitcoin and who ever has access to this foundation automatically have gained access to bitcoin in its entirely, and like we all know, no one has access to this foundation, not even Satoshi himself.
Thing can only turn difficult if the government after owning majority of the bitcoin supply decides to take over the mining of bitcoin as well, this may affect transaction confirmation on the blockchain, but if we have so many miners in different parts of the world, the government still won't succeed in this area as well.