They kept them super high at 0%, up to 4% higher than the equilibrium estimate, which caused inflation to perpetually undershoot and people's careers to be stunted. On top of that, they started giving out interest on reserves which further contracted liquidity.
The growth in excess reserves happened because money being made artificially too good at retaining value compared to private assets, caused people, businesses and banks to hoard it. If central banks would have been sufficiently aggressive at giving it out, they would ironically have given out a lot less because people would not have event wanted that much and instead would have continued keeping their savings in better functioning private markets.
For a large part of history, negative real returns on stores of value were the norm. Before financial systems existed, almost all investments had negative returns if you didn’t put work and energy into them. To store value, you had to accumulate stuff, buildings or land. Most options either had high maintenance costs, were subject to risk of damage from natural causes and theft, were very volatile or required hard labor to get production out of.
The government creating paper assets that have an above market return, puts a gridlock in the private markets and destroys people's lives.
The gold standard was a disaster that lead to the great depression, but that was government manipulated gold.
Gold in a free market would tend to self adjust.
Buying gold as an asset when there is a "flight to safety" and then selling it in better times when there are enough other good assets available such as stocks with good dividends would mean buying gold when gold prices are high and selling it when prices are low thus resulting in negative returns.
Negative real returns happen in free markets. Blocking them causes huge problems.
The real natural rate should be in line with the private markets with regards to safe, liquid short term assets. There is an issue when you hit 0% nominal, called the zero lower bound problem (https://en.wikipedia.org/wiki/Zero_lower_bound). Mechanically you can solve that by keeping inflation high enough that you don't reach negative nominal rates even when you have negative real rates.
