That's one thing. They fear that they might lose control or authority over currency. We know it for a fact that governments intentionally increase or restrict the circulation of money to stimulate investment and spending, generate jobs or avoid inflation and recession; that's why control over it matters a lot. Another reason is the high volatility of crypto. Since one of the duties of a government is to protect its people from scams and frauds, they see more the unsecured facet of crypto rather than its benefits.