Why is fiscal policy sometimes difficult to enact?

People want to get their pet projects through. Many people use voting for candidates that vote for their projects as a method of bribery.

It is very easy to buy votes with other people's money. It is very hard to tell someone no, you are spending too much on something. The problem is further compounded when that money is being spent to feed children who have parents that fail to provide for them with their own sweat and ethical work behavior.