No one offers swapping x shares for y shares, you have to sell and buy.
You can swap currency and some people believe crypto is currency, so it is different.
This is the core of the whole issue; IRS (and similar bodies) are deciding what crypto "is", at least for tax purposes (as is their purview). That has implication for how and when things are taxed.
speculation is treated differently to full-time trading, which is in term treated differently to trying to make some money on the side