If I understand the purpose correctly, the banks are effectively paying investors so that the banks can put additional capital on their balance sheet to satisfy minimum capital reserve requirements (ie more cash on hand in the event of a crisis, which measures were heralded in post-financial crisis). This would mean that they can't spend this cash, although it should free up other cash reserves. The only novelty here is that the banks' advisors have found a way around the twenty five percent foreign tax, drastically increasing the yield for investors and therefore making these investments incredibly attractive.