If all the alleged flying saucer and/or UFO crashes were true, that would mean a vast armada of alien craft was in situ around the Earth.
And many of those vehicles were subject to the whims of Earth’s topography and weather (even gravity) after the vicissitudes of a long journey through space or another dimension, causing them to destruct or crash.
The idea of deficient alien spacecraft flies in the face of a highly technical civilization visiting Earth for millennia.
Either some bumbling alien life force started visiting the Earth around 1947, but didn’t have the technical moxie that earlier space beings had.
Or an alien civilization produced a clot of vulnerable craft for the time period and just made it out of their area of the Universe (parallel or otherwise) and ran into trouble with an Earthian environment that befuddled the pilots of those craft or undid the technology that produced them.
It doesn’t make sense, unless there has been no crashed (or recovered) flying saucers and the tales about them are a concoction of muddled minds or tricks of Jacques Vallee’s metaphorical demons.