If companies paid tax on revenue, then there would be a tremendous incentive toward https://en.wikipedia.org/wiki/Vertical_integration https://en.wikipedia.org/

If companies paid tax on revenue, then there would be a tremendous incentive toward https://en.wikipedia.org/wiki/Vertical_integration https://en.wikipedia.org/wiki/Vertical_integration , because you wouldn't be allowed to deduct the expenses paid to your suppliers.