It's simple: whoever wants capital gains tax from you must prove there was a gain. Without a paper trail, there's no evidence. Can you think of how to make sure that even if someone who sells e.g. property to you provides Bitcoin transaction information, then there will be no way to prove the money you used was actually taxable? I can.
And there's an even simpler alternative: don't spend your money in jurisdictions where capital gains taxes exist, there are a few.
If you dig deep enough there surely will be a way to avoid paying taxes, but the question is how many people are willing to dig that deep, and how many people find it worthwhile to keep looking for alternative routes?
Not everyone thinks like you Carlton Banks. In most cases people choose the easiest and least bumpy road to walk on, and that's paying due taxes. I'm not saying it's good or bad, but it's the reality when it comes to the mass.
Let's say I am a whale with 1000BTC and I'm looking to cash out half of that without nuking a large part of it by paying tax. What jurisdictions are there where crypto capital gains tax isn't obligatory?