or else what? You gonna point your gun at them to pay up? They got a bigger gun than you, and almost every other entity in the world.

Also, getting paid doesn't do you much good nor does it put much pressure on the US:

Before you have some pieces of paper (bonds) that the US issued. Afterwards you have some pieces of paper (cash) that the US issued.

And the US can create arbitrary amounts of cash, if they really have to.

(Obviously, these days it's all entries in databases. But you get my drift.)

Or else I get a free tourist trip to the court room for my free money. Provided the conditions for payout are met of course.

Or else you and other bondholders take away their credit card.