Politicians have a long track record of picking out the conclusions they like from an economic theory and doing some combination of ignoring the preconditions, being unaware of the preconditions, and being too mathematically illiterate to understand the concept of preconditions. I'll leave the exact balance as an exercise for the reader.

If our governments ever ran true Keynesianism, they didn't do it for long before they started spending more when Keynesianism said they should spend more and spending more when Keynesianism said they should spend less, and whatever the academic merits of MMT it has in practice simply removed whatever faint limits the old theories imposed on our politicians because it has been translated to them as "MMT says the government can spend whatever it likes forever, especially if it has the reserve currency, and nothing bad is even possible, let alone going to happen".

In a sane world economists would recognize that explaining new theories to politicians is just handing a lit match to a toddler, but, well, you live in the world you live in, you know, not the world you wish you lived in.