That's true, but it is not very easy to tax cryptocurrency. It is not a physical asset and exists only in digital form. So it is very easy for the users either to hide or manipulate the tax burden. Also, the decentralized nature of the cryptocurrency makes it vary hard to track down the users and identify them. And finally, a large part of the transactions take place outside the regulated exchanges, especially in peer-to-peer platforms.
Technically, it's not easy to tax cryptocurrency. But with the rise of centralized exchanges, it's becoming a "piece of cake" for governments to tax crypto from their citizens via the use of personally identifiable information. If crypto continues to become dependent on centralized exchanges to survive, then its value proposition (which is freedom of money and censorship-resistance) will be ruined. Luckily, we have DEXs, non-custodial mixers, and even privacy-oriented coins to "tackle" this. But the problem is that governments will not allow these decentralized alternatives to continue their development within the mainstream world. They'll quickly classify these "tools" as illegal claiming that they can be used for money laundering and tax evasion. The truth is that criminals use Fiat more for these purposes than crypto as physical Fiat is stable in price and it's much harder to track. Still though, governments don't see it this way which leads them to have a reluctant stance against crypto and Blockchain tech in general.
As long as centralized services within the crypto/Blockchain industry exist, taxation will be the norm of worldwide governments for a long time. Now, imagine if crypto relied on decentralized alternatives instead of centralized ones. If the entire ecosystem was completely decentralized, you could've expected a massive crackdown by governments into crypto by now. The mere fact that most (if not all) cryptos are heavily traded on centralized exchanges, allows governments to tax crypto with ease. There's nothing we can do (for now) but to comply with our crypto taxes to avoid facing fail time. Just my thoughts