Can you give us an example of a country where banks (or the tax authority) would not be consider Bitcoin as an asset? That's definitely not the case here in the USA, and as far as I know it's the same almost anywhere.
I don't say it's illegal, i just say that in france, I haven't seen yet an institution consider your bitcoin as assets of your wealth; THey know it exists, they just don't handle it, you can check any bank form here
Here in the US it's considered like any other security, like a stock or an ETF for purposes of a loan or collateral.
Bitcoin is a highly volatile asset, so that is taken under consideration.