The HUGH problem with a lot of this hot wind going around is that the banks don't 'own' the mortgages... most of them are owned by trusts... and they own a piece of the trust...
And the trust more than likely does not allow the trustee to 'forgive' or 'reduce' principal and/or interest.... their remedy is to foreclose... nothing else... (some have IIRC, the ability to do this for up to 5% of the loans... not enough)...
SO, you have a bunch of trustees who are bound by the trust documents to follow what was written unless they can get ALL bondholders to agree to change the trust... not likely with most of them as they have billions outstanding and all it takes is ONE bondholder to be a holdout...
When I was dealing with other asset backed securities, there was usually ONE small holder who did not want to do anything HOPING that one of the big guys would buy them out at a premium... on one of mine, there was a $2 mill holder on a $500 mill note... would not budge... and nobody wanted to reward him by buying him out...
And with mortgage backs... there are IOs and POs... which have the opposite investment, so they will never agree...