Nothing will make bitcoin to be centralized, it will be decentralized, bitcoin is just like gold, even if the banks are holding the greatest amounts, it is people demanding and selling rate that will determine the price. But, in some aspect, it could be centralized, like governments having policies that any one having bitcoin to be paying certain monthly or annual amoumt. Goverments will try to manipulate and make people depend on them to be able to buynand sell bitcoin so that ways will e looked for to further centralized the coin. But with what I a looking, I do not think bitcoin can be centralized in term of price because the price will never ever be countroled bybcentralized bodies which are governments, bitcoin is decentralized beyond that.
Bitcoin is only a program that is created by the developers, so we are not 100% sure if Bitcoin will stay decentralized over the course of its existence. As much as we hope that Bitcoin will stay decentralized, we are not sure what the future developers will implement. If the consensus of the developers finds that centralizing Bitcoin will benefit its ecosystem there is no telling what they may implement in the future. Let us just hope that Bitcoin stays decentralized and that developers and supporters will maintain it that way.
In short, the word
nothing will make Bitcoin to be centralized is just wishful thinking.