What is stopping all cyclical fluctuations from being eliminated?

If governments can run fiscal deficits of any level, no matter how high, and if these deficits can be financed by money creation to prevent interest rates from rising, why are cyclical fluctuations and unemployment still tolerated? Policymakers could even obtain constant full employment, which most OECD countries are probably trying to achieve today. So are all cycles going to disappear? Will economies remain constantly at full employment (the dream of Modern Monetary Theory) outside highly specific cases, such as lockdowns in response to a health crisis? The answer is no. Such a policy (unlimited monetised fiscal deficits) resolves the question of the acceptability of public debt (since it is held by central banks); but it does not resolve the question of the acceptability of money. The money created by central banks must be held: if it is created in massive quantities to ensure full employment at all times, demand for money will not follow the money supply and there will be flight from money: very sharp rise in the prices of real assets, shift of savings into the currencies of countries that do not practice this policy or into alternative assets.