The deep state doesn't like being told what to do by pikers like Congress and the president of the United States. Tax cuts are hard work! You have to print new forms, learn new answer to questions and get used to things that are different from what you're used to.
Time was when Congress passed a bill and the president signed it, and that was that. But in 2018, the IRS apparently sees itself as a co-equal (at least) branch of government, and wants everyone to know this dumb tax cut simply isn't going to be implemented in full unless Congress gives it a lot more money: