Earlier quoted context omitted.
Not everyone earns money via income. You have to define what "income" is exactly, then it starts getting complicated...... Example: I route my investment earning via a company, that company can claim expenses such as paying my utility bills and buying my groceries, anything leftover they give me. They work it out so my net income is zero, oops. It's easier actually to tax purchases.
Taxing consumption would rapidly explode into a vast array of categories and rates for different types of consumption, luxury taxes, etc. Food, maybe no tax. But maybe there's some tax if it's ready-to-eat. Or based on sugar content. Automobiles maybe taxed rather heavily, but the first $5000 is exempt so poor people can buy cheap cars, etc. It would become just as complicated as the current code.
It's an entirely byzantine system, but because it's happening when products are imported, or at the point of sale, it's vastly easier for consumers than an equivalent system that works through tax rebates.
Things on that list occasionally become a political issue. E.g. the tax on added sugar has gone back & forth a couple of times depending on who's in government.
Still, this adds zero complexity to your tax return, or to the average person's interaction with the government or private businesses.
1. https://www.tollur.is/library/Skrar/Tollskra/Tollskr%C3%A1%2...