I travel to India every year, and I always carry with me a few hundred USD worth of rupees (the local currency).
It would be insane for me to try and track the value of the rupees (in USD) for every time I bought something, and calculate the deltas between that and what I originally gave to the money changer. It is completely impractical to do that, and while I'm not an accountant, I have an intuition that for any reasonable amount of money that any traveller would be carrying with them, the fluctuations are irrelevant.
And yet this is what people using cryptocurrencies are expected to do.
Obviously if there is a large capital loss or gain, then this should be reported on your taxes, and I suspect the same is true for foreign currency exchange.
I guess to ask a question: are individuals expected to track the fluctuations in USD value of their cash while travelling? If so: is there a threshold? Why is crypto different (other than some belief that it might be more convenient).