Big Banks
The big banks have a responsibility to share holders to make profits and the easiest way to make profits is to create money by issuing loans for mortgages. They have almost no risk when lending mortgage because the house is an asset that can be sold and there is insurance if the loan to equity is greater than 80%.  The graph below shows how house prices have almost doubled relative to earning in the last 25 years making housing less affordable. Its not the banks fault, it is the monetary system that makes them do this that is at fault.