I think the main reason is Cryptocurrencies can be used to hide assets and income, making it challenging for governments to collect taxes. This could potentially reduce government revenue, which they rely on for public services and infrastructure.
Maybe it's like that. But actually hiding assets or the like is even easier if they are in fiat or gold. Because there will be no written data if we transact offline with fiat and gold. So we can store gold and fiat in a large safe underground without anyone knowing. But through cryptocurrency every transaction is recorded in the blockchain and it can be traced in fact I feel it is more transparent than the usual fiat transaction process.
Even crypto wallet ownership can ultimately be traced if it has a transaction history with a centralized exchange that also uses KYC or something similar.
And actually it would be better for the government to implement clear regulations on crypto so that they can get tax income from every transaction carried out on an exchange registered with the government. And even if the government is hostile to crypto then this will only make its citizens transact secretly. And in the end the government will lose because it doesn't get any tax income. If regulations regarding crypto have not yet been made.
Even with its enormous potential for revolution, cryptocurrencies arent a perfect solution to all of the world's financial problems. The claim that gold and fiat can be concealed more successfully? Yes, on the one hand, no digital footprint was left. Physical assets, however, are subject to seizure, theft, and destruction.
You are correct: every crypto transaction is recorded on the blockchain. Do not deceive ourselves, though. Privacy coins and anonymity techniques are available. They have the ability to obscure transactions, negating the transparency of public blockchains. But who right now are currently use advance crypto like Monero?
Furthermore, the notion that states had to merely "implement clear regulations"? Said to be easier than done. It goes beyond tax income alone. It has to do with international commerce, crime prevention, and financial stability. Instead of oversimplifying things, its time we faced the reality of the situation.