people tend not to believe in things they never see personally even if there is evidence. For example if you look up the history of the panda bear they were like a mythological creature for decades, nobody could ever find one even though they were claimed to exist they weren't 'discovered' by the 'official scientific community' until after they had searched for decades and given up looking, one turned up.

I've seen UFO's that don't fly like a plane that requires wings and aerodynamics to get around. So I believe that UFO's are real even if they are man made. Also statistically its a big universe and there could be intelligent life on any of those billions of stars and it could be older and more advanced than us by a longshot enabling them to cross the distance we think is impossible. It's far too unlikely for aliens to not exist.