Okay, well let’s apply that newly specified set of requirements.
Earth must be flat for the same reason. There’s even more evidence for it than for aliens, across history, across continents and cultures, and there’s plenty of content regarding it in the modern world too, independent of any specific locale.
Do you believe the world is flat?
Okay, so now that the requirements are even further defined, let us continue applying them.
God must be real.
Do you believe in god?