The practical reason is that this would penalize smaller companies working together over large, vertically integrated ones. If company A sells an item for $10

The practical reason is that this would penalize smaller companies working together over large, vertically integrated ones. If company A sells an item for $10 and buys $8 in parts from company B, who buys $6 in parts from company C, the total taxed amount will be $10+8+6 = $24, while a totally vertically integrated company would only pay tax on $10. You can get around that by only taxing the value added ($10-$8 etc) which is a VAT tax and a popular way for countries to raise revenue. The bigger issue is companies transact with consumers, workers, and shareholders. But when you have a tax, what matters is really what transaction you tax and not which side of the transaction pays the tax. For example, payroll and income taxes both reduce wages. If you tax revenue, that's basically taxing the transaction from consumer->company, so that tax (VATs, sales taxes, etc) falls on the consumers.