Because there's no evidence either way. It's valid philosophically to consider the unknown or unprovable statement to be false, but the philosophers of science

Because there's no evidence either way. It's valid philosophically to consider the unknown or unprovable statement to be false, but the philosophers of science have pretty soundly rejected logical positivism[0] Generally speaking the problem is that we can't treat empirical truths as some sort of strictly binary, completely true or completely false statements. Error is inherent to observation, so every scientific truth is a little bit false (or at least potentially so). The less rational part of me does consider that chocolate tapdancing unicorns are unlikely enough to be entirely discounted, but as a general philosophical rule it's more consistent to be a little more humble about what is known and can be known. [0] https://en.wikipedia.org/wiki/Logical_positivism#Critics https://en.wikipedia.org/wiki/Logical_positivism#Critics