The debt matters to the extent it drives deficits but otherwise it's just a number.
Deficit to GDP are more interesting ratios because they're both vectors (debt is a scalar, it would be like comparing miles to mph). Debt to wealth would be an interesting ratio.
The other factor is that the world financial system is basic built on t-bills and when they tried to find something else to use it ended up pretty badly.
One day the Ricardians may be correct but they've had 200+ years of being wrong at this point.
Ultimately all money has to be made up. Gold is a useful industrial commodity and it goes well with Persian skin tones but its value as money is only far beyond those things because a bunch of people agree that's how it should be. Greenbacks are no different. And, unlike gold, greenbacks are backed by the full faith and credit of the US government which only morons try to fuck around with. Along with the biggest and best performing large economy in the world, the second largest nuclear arsenal (and who knows how many Russian bombs actually work) 11 actual aircraft carriers, 10 more ships that pretty much every other country on earth would count as aircraft carriers a fuck ton of nukes, and a seemingly insatiable appetite for consumer goods.