i think this is the result of Bank Negara's payment card framework which came into effect January 2 2015, which reduce the interchange fee issuers can charge. In this case, banks are earning less, hence they have to pay out less too.

My CIMB Bank points oso suffered inflation too. I think other banks will eventually cut down their cash back. The best at the moment is OCBC card with 1% cash back and 1.2% cash back. they will cut too.