Tax Evasion, Plain and Simple
nytimes.com
nytimes.com
And the argument that the tax system in the US is too complex for trillion dollar companies to navigate is laughable. That's arguably very true for individual taxpayers but Apple isn't parking billions in Ireland through a Double Irish Dutch sandwich because the American tax system is too complex.
The global minimum tax rate is only 15%. As you said yourself, as long as other countries offer less tax rate, they will continue to shift profits elsewhere.
Providing a simpler tax system might not stop Apple from shifting profits, but it definitely increases the incentive to do so.
I don't think it does. As parent said, they don't do it because of complex tax system, but because of lower taxes. Why would they choose to pay higher taxes if they don't have to? What is the incentive?
If you look at app stores, etsy, amazon, etc. they all take a 5-30% cut of revenue before any costs and expenses are considered, and it seems to work for them.
Europe's value-added tax approach seems like a better alternative, though I'm sure it too has drawbacks.