Banks aren't charities. It costs a good bit of money to keep deposits, on top of the interest expense. (deposit insurance, overhead, staff, etc...)
I think it's highly unlikely that these overseas banks that the rich use are doing nothing but sitting on their money and this practice accounts for all the purported "hoarding".
From the St. Louis Federal Reserve: "Lending growth slowed to zero during the 1990-91 and 2001 recessions but recovered after a few quarters. In contrast, during the Great Recession (2007-09), loan growth became strongly negative and remained so for almost four years."
I think it's highly unlikely that these overseas banks that the rich use are doing nothing but sitting on their money and this practice accounts for all the purported "hoarding".