The international financial system makes it very hard to "run away" from a loan. Unless you are genuinely willing to become a wanted fugitive, you will end up having to pay.
There are a non-trivial numbers of absconders hiding in the US and the UK. The most famous example: https://en.wikipedia.org/wiki/Vijay_Mallya?useskin=vector
The amount of money and effort required to extradite a person far outweighs the average student loan. Not only that, it is not really a "crime" to not pay your debts. It is a civil violation. The court can seize your property, in limits. You can't seize someones house in some states, and some don't even allow you to seize cars. Even if they can, any given student loan holder may not have either.
Y'all have the delulu American exceptionalism brain. People will leave if they don't like living here. A loan eill not stop them.