It has everything to do with the actual currency, if people weren't buying dollars at the rate they do to do commerce the US could never run the debt it does, it would have crushed any other country.

It also means Americans get to buy stuff from all over the world cheaper than anyone else, the moment this goes away inflation for imported goods will eat into people's salaries, there will be less investment as it will be risky to invest in a country in a debt crisis and folks will find out what it is like to live in Argentina for the past few decades.

The quality of life loss in the country if this happens will likely get people to stop talking about the great depression.

Knowing you will get paid back (i.e. credit worthiness) is part of it, but another part is that the currency holds its value, and the global demand for dollars is an important part of that. If the global demand for dollars decreases, then borrowing is more expensive because you need to offer a higher interest rate to entice people to purchase bonds, because they have other more attractive options to store/grow their money than US bonds.

One way to think of it is that the US benefits from the current world order by essentially taxing the rest of the world to pay for its spending by devaluing their currencies relative to the dollar.

Yes and no. US can just print more dollars and pay its debt, which it is doing since Nixon. It doesn't need to default on its debt ever, as long as USD is the reserve currency. Of course the rate rhis happens is a delicate thing. Too quick devaluation would upset the debtors. Though they own so much of US debt (like China owns 2 trillion dollars or sth) that they are incentivizes to play along.

At the end of the day, somebody out there has to have a US Dollar and feel comfortable lending it to the US Government. The reserve currency status of the dollar means more people need it, which means there’s more supply of dollars to borrow without causing currency collapse.