My take on this issues is that no matter how they tried to hide bio or mio in their wallet through bitcoin one day it will still reveal itself that they are looting funds. We know that is a decentralized platform whereby we can't trace or track them so they must sign up in exchange to buy it them selves but through their kyc exchanger may still know that a prominent politicians owns such amount in their account. And even if they thought of buying it through p2p there are some fellow youths who would still come reveal about their transaction with such politicians. Currently I know that youths are angry and if they discovered such thing they will raise alarm to Nigerians how politicians are using our money to buy bitcoin in other for them to loot.
One of the major reasons why most countries government are having missfeelings about Bitcoin is due to the possibility of the politicians using Bitcoin to melt away national wealth, but not knowing that politicians have employed a lot of alternative ways to steal money without traces aside from using bitcoin since it can still be traceable to them.
More also you are right that the decentralized nature of Bitcoin and other cryptocurrencies that we have around have made privacy really achieved for some limits and most of the corrupt politicians are aware of that and they are holding huge amount in both Bitcoin and other coins, I remember when cryptocurrency was first attacked in Nigeria, we had a lot of politicians with cryptocurrency trading apps on the mobile devices so it shows that they already know what the new development really is.