Many of the workers in the IRS offices are temps, hired for the tax season and laid off afterward. Yes, they might have degrees in accounting and they might have done the work last year but the tax code changes annually and they might not be "up" on the latest changes.
(I know this because when I lived in the Cincinnati orbit it was a Big Thing for unemployed professionals to hear "the IRS is hiring!".)

Why not a simple code?

No deductions for anything for anyone -- not for kids, not for churches, nothing for nobody. You pay, say, 10 or 15% of everything over $10,000 (to help the truly poor, kids with lemonade stands, etc.). No cap -- you make a million over 10 grand, you pay $150,000 in taxes.

During a declared war the amount paid can be adjusted upwards, and the increase stops when the war ends.

It would be a truly graduated tax -- the poor pay less than the rich. It would be understandable, it would allow people to plan ahead, and it would put tax preparers and accountants out of business.