Because banks aren't transparent, and many countries don't want their banks to be transparent either. Honestly, this logic is similar to blockchain—some people want blockchain to be more transparent, so transparent that they wish they could know the identity behind every single address. Personally, I don't think banks are afraid of blockchain. The ones who should be 'afraid' of blockchain are the governments controlling the banks. For example, if we know the address of certain malicious organizations, we could trace it back to the banks, the countries, and even pinpoint the individuals transferring money to these organizations. Banks are invisible to the public, but as long as the government can see them, that's enough. On the other hand, with blockchain, once you discover the fundraising address of a terrorist organization, you can trace which chain, which exchange, or even which wallet was used for the transfer. And then you find out one of the addresses belongs to a central bank of a certain country. That's hilarious.