I think much of it is the "hawthorne" effect. Everyone in Ireland see leprechauns. Everyone in Pacific NW sees bigfoot. Everyone in Mexico sees Chupacabra's. After WWII the rise in sightings is what caused the hockey stick to rise from sightings.
I am NOT saying this is THE explanation, but I discount most of these as sights of what people expect to see now that the zeitgeist is established. Radio controlled drone technology goes back to the 30's. I do think most of these sighting are military in nature, but that alone isn't to say the vastness of the universe is to be discounted, but if you can travel billions of miles, your "ship/probes" are blinking lights and saucers easily detected with the naked eye?
My tongue in cheek earlier post about laser pointers was about creating the perception of a thing using illusion and deception - two of the oldest tenets of warfare. You "think" you saw something, and you act upon it. Now you see it, now you don't....
None of this helps Russia in Ukraine, as it's a conventional war of attrition. Doesn't help China either as they will invade Taiwan from within. It's a fortress with no accessible beachheads and a Chinese navy without landing craft across 100 miles of rough ocean.