Are you asking why any country is able to impose a tax on its residents? Morally, because they owe an obligation to the society they live in. Practically, because the state has a local monopoly on violence and may jail them unless they pay.
It's so easy to say "moral" but I struggle to see the moral principle at play. I understand paying proportionally to resources/wealth in that country. I understand paying progressively for those or income in that country but why pay in proportion to what you have already build in another place?
It is proportional to the resources you use in every case where that is possible. It is nonsensical to say "Well, you used only 2% of police time this year, so that's how much police-tax you'll be paying", not least because it is impossible to put a "usage" on the benefit of having police in the first place. Where it is possible, like how much land you own, you are taxed proportionately.
This is analogous to asking why should software be priced on value delivered, vs priced on costs incurred in producing. Value pricing is much more common.
The value you derive from living in the country of your residence is higher that your poorer neighbors; hence you are charged more.