And not only have they crashed, they have somehow yet to make their presence known on a large enough scale to enough people. They apparently always want to land in the desert or in the ocean, instead of where the artificial light emanates the brightest. Imagine if we somehow managed to travel the stars and stumbled upon an alien planet, and instead of landing where there were massive buildings and seas of artificial light, we landed miles away where there is nothing... it just doesn't make logical sense.
Like, devils tower is a really cool premise for close encounters of the third kind, but I think they'd be more interested in the burj khalifa (or the world trade center back when the movie came out)