I live in a very corrupt country, but interestingly Bitcoin has never become a topic on that matter. Every schemes operated by politicians so far have been done through fiat currencies, consolidated banks and the participation of government's agents. It means they use the centralized system in favour of their schemes of corruption. Centralization is so good for them that they don't feel like a decentralized currency like Bitcoin is necessary.
Silence about politicians buying bitcoin does not mean these politicians completely do not invest in Bitcoin or cryptocurrency. And take note, bitcoin blockchain is transparent, imagin if a politician use Bitcoin to launder money, then all his actions will be recorded and can be proof of the person's corruption. Fiat money is still the best way to launder money.
Ironically, centralization is promoted as a way to restrain criminal activities, while decentralization is identified as fertile soil for scammers to operate.
This is what the government wanted to inculcate in the minds of its citizens. They have to promote that their policy is solid and can avoid fraud and lies about the system that does not follow their protocol.