All of the banks, at one point or another in the past two years,...

All of the banks, at one point or another in the past two years, have used underwritten dividend reinvestment plans to fund their dividends. That means that even if you choose not to participate in the DRP, the bank will issue new shares to the underwriter to pay the dividend to you - ie the bank makes a net payment of $0 because the dividend is entirely financed by issuing new shares.

So part of that 10% grossed yield is an illusion, because banks are issuing new shares and diluting existing holders to keep their dividend yields so high