Mining bitcoin can be centralized but that does not mean that bitcoin is getting centralized, this one issue with mining bitcoin is the regulation challenges from government since they can present themselves decentralized since they majors their energy source from government supply, if they mine bitcoin doesn't change the fact that it's decentralized since everything occuring is within the blockchain network, the only way you can have your bitcoin centralized is now depending on the source you're acquiring it through and of course the kind of wallet you used, miners have physical location to get them been identified for that purpose and this makes them centralized and not the bitcoin, just as every whales out there will think loud of much accumulation of bitcoin because they have the capacity to do so but that doesn't change anything to bitcoin been centralized.