Because they are residents of Earth, and Jesus instructed his disciples to spread the gospel throughout the world.
So we’re all guilty because we didn’t invent time machines to go back to the year 1000 and preach the Gospel to the Aztecs. I suppose that since we got our lazy backsides to sub-saharan Africa around the 1700’s or so and started preaching the Good Word to the natives meant that magically their ancestors also are saved.