It's because they're trying to give people breaks on what they owe. The more money you make (and the more ways in which you make it), the more exemptions and breaks you tend to be eligible for, so the more complicated your taxes tend to be. A realistic simplified tax code would probably mean you, as a senior engineer, would pay much more in taxes, which would be fine with me! A properly-funded government can be a great boon to society. But you might not feel the same way, so be careful what you wish for.
Governments that can print money don’t need taxes to be funded, they can just print money. Taxation is more useful for redistribution, incentivizing behavior, and controlling the money supply/inflation - not funding the government.
