To me, the idea that it's "political" to use the US debt, is on its
face hard to believe or take seriously. So before everyone else has
to justify every other claim down to many levels of detail, can we see
any justification of the claim that there's any disadvantage to using
this convenient number, or that it's done for political reason?
Occam's razor suggests it's just being used because it's convenient
and easy to use and meets the criteria, and once it got into the mix
there was no reason not to keep it the next year, or the next. It's
easier to keep things that still work, than it is to spend extra time
searching for replacements for no particular reason or advantage.
-- Cos