Margins almost always increase anyway.

I'm not sure anybody fully understands the mechanism (for the most studied phenomenon of economics, inflation is quite badly understood), but that doesn't change the fact.

Anyway, if you run the Keynes model for macroeconomics, the average margin increases very naturally when the money supply increases. It increases even more if the new money is injected in the economy by well distributed government spending. Still, that's one model we have that kinda works, but it's so full of problems that you can't take its predictions for granted.