And the more left-leaning part of the aisle has this idea that they will get to decide what that money will be spent on. So they support this. (I'm not rightist, in fact I'm probably extreme left by American standards, but I just don't believe the government is on the people's side anymore)
Of course there's a million different ways to say this, many are more polite, but it all boils down to this. They want money, they have the ability to take it.