I can’t imagine Congress critters finding problems in tax returns AFTER they have been approved by the IRS. They are just FISHING.
What I’m mostly thinking of, is you have to give the IRS a lot of information about your activities and resources, which you would consider private, and which you would make it difficult for some adversary to see. If a rival can just walk over to the IRS and get your tax returns, they’ve got a cheap advantage over you, at least potentially.