Why the typical "alien" looks remarkably human, [...]
The same reason all of our gods look like us: we anthropomorphize our myths and fantasies. We project our own qualities on the mysterious in order to make sense of it.
One need only look at the anthropomorphic habits of cartoons to see good example of this: Sponge Bob, Wile E. Coyote, etc.
Cultures have been variously applying animism, totemism and the like to animals, objects and even the weather for centuries, creating deities, creatures and spirits that have human qualities and characteristics. Be it a volcano, a jaguar, a jackal, or a god of thunder swinging a hammer, they all have features that mimic our own: hunger, lust, bipedalism, tool use, etc.
There's no reason to expect that wouldn't also continue this projection on space aliens as we move into the space age and come to the realization that the universe is a big place and there is likely to be a multitude of life out there somewhere.
There's also the effect of pareidolia where humans see an object or pattern and recognize human characteristics in it. The face on Mars is a good example. So are the various shapes of Virgin Marys on sandwiches and tacos or the spillways of highway underpasses (calcification and discoloration from water dripping the wall from a drain).
We anthropomorphize unknown aerial phenomena (headlights on a low cloud on a dark night) by expecting an intelligence to be flying it since its in the sky. The intelligence behind the light is actually on the ground, yet the observer is unaware since this sort of observation has never occurred to him/her.
The subsequent sighting of the shadows of deer in a field where the light seemed to "land" brings about the expectation of these "intelligent" beings. We then
project or
anthropomorphize ourselves on the shapes -our brains filling in the patterns with what we
expect to see: bipedal forms, standing upright. But its dark. We don't really see the scene in a good light -the brain is making up the difference.