They also leave no room for "cheap" campaign promises and new initiatives that politicians can announce and display to the media (repeatedly). We'll give a tax credit for low emissions vehicles to save your children's lungs and the planet! An incentive to finance homes for nurses!
Tax is just code. Poorly architected code with lots of documentation that obfuscates rather than illuminates.
Politicians love to nudge through the tax system as it seems cheap, costs are obscured as, and there's no project to fail like there is if you try to build something. You end up with perpetual scope creep and "minor" additions.
Then you get people politicizing the outcomes - "bad people" are taking advantage of a good program, or a "bad company" isn't paying as much as someone thinks they should in an ideal world. If you are going to live in a nation of laws rather than the whim of some functionary you need to let everyone do what is legal, rather than just preferred individuals or classes.