It actually does when talking about pre-existing obligations denominated in the currency. It doesn't when talking about most other things, but existing pension obligations are pre-existing dollar-denominated obligations.

Now, the feds monetizing all the underfunded state and local pensions would effectively devalue the dollar, so those pensioners (and everyone else on a fixed dollar-denominated income) would be getting far less than they expect for it, and taxing extra money out of the system to counteract the inflationary effect negates the whole idea of monetizing the obligation in the first place—you might as well just leave monetary policy alone and tax money out of the system to pay for the pensions.