The real point I want to make is in order to simplify the tax structure, you rob the politicians of their main economic design power. No more tax incentives for solar, high efficiency windows, developing in high crime areas, and the like. I'm willing to pay that price, but are you? (The royal you, i.e. us).
The final point, the real crux of the matter, is that politicians cannot predict all the consequences of the tax breaks they create. If tax breaks exist, people should try to get them, otherwise the whole incentive structure doesn't operate. Then some people who were not intended to get the break find edge cases in the legal language to exploit. If the politicians can't predict all the edge cases of the incentives they design (which they can't) then we end up with things that seem outrageous until you read the law and go "oh, that's the loophole. Shitty, but seems legal.". This is why the federal code is so complicated. People making the tax code more complicated over time to try to specifically target the incentives. Just like a legacy codebase, in fact. Except that it's subjective when you evaluate it.
Edit: typos