Who decides what “a people” is? You have a bunch of people in a geographic region, and some of those people get to decide that they are “the people” and that only they get to vote? Sounds pretty blatantly undemocratic.
You make it sound as if they just happened to wind up there at random, and have nothing else in common.
Geographic proximity is incidental to belonging to a group. The land they live on is merely one of their possessions. Allowing visitors does not mean they must share their sovereignty with them.
To answer your question, in democracies, each person can vote to influence their own nation - their demos, even while abroad. You think demos should be decided purely on current location, but most countries disagree - they use mostly jus sanguinis, with the exception of jus soli in the Americas.
I understand the historical reasoning for some of this stuff, but as long as the laws apply to everyone in a physical location, I think the only way to claim to be democratic is to let everyone in that physical location vote to influence those laws.
