This is why I don't think we'll ever see tax code simplification: there are too many people making too much money with the existing overly complex system.
This is not just a problem with the tax system, it's a problem with the US legal system in general (and not just at the federal level).
The legal profession, as a class in society, is in a position of ethical conflict of interest with respect to the complexity of the legal system.
Most legislators are legal professionals. Large numbers of legislative staff members are also legal professionals. The prosecutors that decide what aspects of the legal system to enforce are legal professionals. Most judges are legal professionals. In short, we have huge numbers of people with a vested interest in having a complex legal system.
As a result of this ethical conflict of interest, the US legal system is an unmitigated disaster.
Note that the mess we're currently in isn't the result of conspiracy. There aren't any secret meetings in the dead of night. It's just the result of individual decision making over many decades by a lot of unprincipled, self-centred, and short-sighted people. If anything, it might be that the best way to look at this is in terms of entropy in the system.
The only difference between the ethics problems in tax law and, say, Constitutional Law, or Contract Law, or Copyright law, or Patent law is the makeup of the specific groups with their hands in the pie. For tax law, it's the legal profession, the accounting profession and certain companies, plus those wealthy entities in society that need a complex tax system to hide loopholes in.
The right to ethical practice of law and ethical government is certainly a right retained by the people (9th Amendment). Even the appearance of conflict of interest must be avoided whenever possible.
It follows that a) the current tax law is unconstitutional, and b) any legislators that accept lobbying funds in return for preserving the current system are in violation of their oaths to uphold the Bill of Rights (oaths which happen to be preconditions for holding any position of public trust or responsibility).
Further, any legal professionals involved in a lobbying effort to preserve this unethical system are in turn in violation of their oaths to uphold the Bill of Rights (which happen to be preconditions for being licensed to engage in the practice of law).
Rights retained by the people being retained by the people, any precedents to the contrary are null and void. Putting that in other words, if the legal profession could decide it didn't have to be ethical, or any group make up of legal professionals could decide this, there wouldn't be any rights retained by the people - a contradiction.