I mean, there are countries where tourists don’t have to pay tax on top of items (meaning they pay for it tax free given if they presented their passport upon purchase proving they’re merely only a visitor, that won’t work on expats though). Those countries usually have tax refunds when visitors are leaving (basically reclaiming VAT whilst at the airport).
Three states (Louisiana, Texas, Washington) do that. Others don’t.
As to why, the simple answer is the state government made a law. They get to do that because the state constitution says so, and it doesn’t conflict with any federal law. If you keep asking why, you’ll usually end up with a root cause like the people who have power want it that way, or at least don’t especially want it a different way.
The fact that other places do it differently has nothing to do with anything.