HELP! Why did Obama do this?

Two separate issues. Congress can't raise its own salary....it can only raise the wages of the NEXT congress....that's in the Constitution. 27th Amendment. Public employees wages are set in conference with members of a civil service pay and benefit commission and union officials. While the president may 'announce' the results of negotiations, he personally doesn't set pay scales or have anything to do with that aspect of the civil service.