Why do you assume they can track it only from overseas?
They can track every payment as long as the final step happens in their country, if I send my friend a 1000E payment now via a bank transfer they will know. If I send him 1000E via PayPal he must do something to get that money from Paypal and it will end like all 3rd party payment processors with a link to your bank account and get tracked.
P2P anonymity is highly overexaggerated around here and I don't understand why, transactions between people who don't own a business and are not related by blood or don't live in the same are standing out like a skyscraper in the desert, how many normal users do you think are making more than 20 transactions a month with complete strangers? None? Once they track a node (a trader on lb or bisq or whatever) they can link everyone who has had deals with him and it already happened tens of times.
Second, with taxes it's not the government who has to prove that money is from crypto, it's you in the first place that needs to tell them what are that money is for, and falsifying a document is a felony, that's what is stopping a lot of people.