The operating idea from governments is that in the digital age, when you sell something to a customer abroad, you're selling to them on their turf and not yours. That's why you're considered liable for sales tax in the first place. Doesn't matter that your own country of residence may or may not care. For all intents and purposes it's as if you physically flew to the country and hand-delivered your software/product to your customer.
It's clearly an awful "patch" to outdated concepts on how commerce works compared to pre-internet, but it's what we have right now.
