Why are there so many human extraterrestrials?

My theory is that there is only one planet that had humans (besides us) in those universes. They found other planets, then used their hyperspace drives to get there, while going back in time several million years. Then, they enact terraforming measures that will take several million years to do. Then, they travel back into their present, then they can migrate to other planets. A few centuries (heck, decades, even) later, the cultures on each planet have independently developed into something entirely different. It doesn't take long here.

In fact, we might have settled those planets using the same method, but sending colonists back in time...thereby bypassing the "how did humans develop on more than one planet" conundrum also.

Now about alien species...other species developing on that (or this) planet, or genetic inbreeding, or genetic engineering.

wait, do you mean that the aleins went back in time and then their civilization started and then this civilization turned into the one that went back in time? I'm confused.

No, I'm saying that civilization originated on one planet. Then, through millennia, they created hyperspace drives and time travel. Then, they terraform a crap load of other planets a few million years in the past. Then, they send colonists there in the present. Wait a few decades, and you have the mix of misanthropic civilizations we have on Earth today. Which is basically the premise of any sci-fi media.

I have this crazy theory that it is much easier to make a costume consisting of just a pair of pointy ears and a wrinkly nose and stick it on some actor,than it is to completely imagine and animate something non humanoid.And it is much easier for authors to imagine something of humanoid shape,than something as wacky as a ball.

Seriously though,when you say any,you are wrong.Any lazy would be the correct term here.There are many good sci fi writers(for all media,not just books and tv)that dont go the humanoid paths.Ive read about sentient balls,etheral beings that have sex in threes,dragons,lizards,even sentient planets.Ive seen much less of such great ideas though(and odly enough,men in black is,at the moment,the only thing coming to mind where aliens are not all humanoid),but Ive played lots of video games with extremely weird extra terrestrials.

Good point, true. But I was trying to cover the reason why there are so many alien (humanoid especially) civilizations in the present, now, with different cultures, etc. And genetic engineering could have taken care of the non-humanoid species, though it does stretch my theory a bit.