> Can somehow add a layman explanation on how Americans can be so much in debt but have good "credit score" that allows them to borrow even more?

A credit score measures the risk of **not making monthly payments**.

That's all.  Nothing more.

If a creditor thinks you're a larger risk, they'll likely just demand a higher interest rate, or some form of collateral on the loan. Assuming they're wiling to take on that risk.