I'm a computer programmer that has started reading Schumpeter's "History of economic analysis", but I think not even a guy like Schumpeter could have explained

I'm a computer programmer that has started reading Schumpeter's "History of economic analysis", but I think not even a guy like Schumpeter could have explained why at some point in 2019 more than $17 trillion were returning negative rates (and I don't think that sum has decreased by all that much).