The fact is that we have no idea if or what forms of life might exist in the universe. Yet you're proposing that we presume none at all until "proven" otherwise. That's the logic of an atheist.
There are very clear differences in the two situations.
In one, we know what sort of technology would be required to answer the question. We simply don't have that technology as yet. And, at each stage in learning about what life is and how it works, it becomes *more* probable that other life exists in the universe.
In the other case, at each step, the explanations relying on deities have been shown to be wrong and other, better explanations have been found. We no longer attribute diseases and lightning to deities, for example. At each step, the 'gap' in the 'god of the gaps' has narrowed, not widened. At each stage, the 'god' explanation has been found wanting. No technology, even in theory would be able to show the existence or non-existence of a deity.
So, in one case, it is reasonable to think that the question is open while in the other case, further search is unlikely to provide evidence.