If they manage to control more than 51% of Bitcoin's hashrate, the cryptocurrency will effectively become centralized.
You either don't know what centralized means or don't know what having 51% of the hashrate means.
Owning hashrate won't centralized bitcoin, they won't even be able to censor bitcoin transactions because the remaining 49% will still mine your transactions.
Besides you are forgetting that bitcoin is a global currency not only operating in one country. If one government started building up its hashrate, others will do the same too so we could essentially end up with multiple governments each owning a tiny portion of the hashrate like 10%.
That, and the fact that they already control centralized exchanges is a very alarming situation for the future of Bitcoin.
Same arguments about hashrate but additionally centralized exchanges have nothing to do with bitcoin!