Its a very political field and whichever little clique gets the ear of the decision makers that year determines what policies get enacted. I'll grant you that this doesn't matter in practical terms, because we all know that the policies will benefit the rich, not us, but at least you can get a better understanding of how you'll be robbed.
This is needlessly antagonistic towards economists. The majority of them are boring academics. The others are employed by the rich to whisper into the ears of politicians as you describe. This is precisely why it's important to learn economics: so you can vote for economically literate politicians who are be better resistant to lobbyists' BS and vote against politicians who are clearly trying to favor special interest groups.
They listen to the ones they find useful. I guarantee you "trickle down" wasn't Bush's idea, an econ man put those words in his head, and it was to provide academic justification for giving the rich a big wealth transfer from the working class.