The tax code is this way because in practice everyone wants it to be this way. We spend through the tax code instead of directly paying for things because it's a lot easier to sell politically. People say some variation of, "Make my tax code simpler, but don't get rid of that deduction over there, it's important to me." There are literally billions of dollars spent making sure deductions stay exactly where they are every single year.

Given that complexity and what I firmly believe to be its intractability, this is a hacky but OK solution to make taxes less awful for most people.