The credit system is not important. When I came to the US I didn't even know what "building credit" means. To me being creditworthy meant not to have debt.
Sufficient (positive) net worth definitely makes someone creditworthy. But, most borrowers aren't leveraging major assets like companies or investors or others might. What they're leveraging is their future earnings. "I need $10,000 today to buy this car, and over the next 3 years I'll pay it off at X% interest." Having a history of using credit effectively in this manner (paying it off on time being the big issue) is the only way that someone without a significant (positive) net worth can demonstrate to a lender that they're creditworthy.