There is more going on in Sumner’s article than ignoring incentives of public choice.
Sumner is trying to figure out why the bulk of *economists*, not politicians, are throwing out their textbooks and instead going along with governmental ineffectiveness, or stupidity, or capture if you will, in dealing with a problem that can be differently framed as a nasty reduction in the velocity of money, or a radical increase in the desire to hold money, or a recessionary decrease in AD.

Unless I am missing something, public choice doesn’t explain why academic economists have suddenly chosen to abandon decades worth or economic theory. Scottsumner is merely trying to explain to his peers why they erred, not why the elected government erred.