If you paid an external company to make all those things for you, they'd have profit in all those places, but if you do it in house, the profit just moves to the point of sale?

Why not replace income tax with VAT/sales tax if sales is the basis of taxation anyway?

That doesn't account for infrastructure/governmental costs associated with creating the stuff that makes the profit. As a hypothetical, if a German company writes some software and US companies are the only ones that buy that software, the US harvests 100% of the taxes on profits while the German government is left holding the bill to take care of the roads that lead to the office, electricity infrastructure, employee's healthcare, etc.

It puts the government in a weird spot where they really don't want any businesses that primarily sell to foreign countries since they don't get tax revenue to fund public services for that company.