What stops somebody from interacting with a foreign company that exchanges crypto and $LOCAL currency? Sure, the entire ecosystem would take a hit, but also no

What stops somebody from interacting with a foreign company that exchanges crypto and $LOCAL currency? Sure, the entire ecosystem would take a hit, but also note that many US companies have actually bought Crypto, people recently bought crypto on margin, and, those who still own crypto, can exchange it outside $COUNTRY, and convert currencies.