I think it all starts pre-birth.
Even before you are physically born and put on this world, you got consciousness and started to build an egoic mind.
During your whole life up to now, you have been influenced by your surroundings, both conscious and unconsciously so. In fact, your surroundings have pretty much made you who you are. Your ego has grown, you got certain values and you grew up with the idea that this world exists and it exsists the way you have been 'told' it is.
I've had exactly thesame thoughts about this that you have. If 'I' create this world, why is it so bad?
Then again, would 'bad' exist if you were fully conscious? If you were one with being? If you experienced being to it's fullest every day?
The answer would be no. If you are one with being, I think you would be at all, well not like you are now anyway.
So my guess is that we are just not fully conscious and thus are led for a large part by our egoic mind, which tells you the world is as it is.
If you would be able to consciously create all that is, then you wouldn't talk about 'me' or 'I' in the first place and you certainly wouldn't have to ask the question why..)
What Adam said, that's basically it. So let's start cleaning indeed.