why did God make them that way?
I believe it is a direct result of the fall. I did a (rather poor) blog entry on how God hides Himself. The fall wasn't just man becoming corrupt, it was a separation between man and God that was not present at Creation. I believe that separation is - at least in part - a mercy on the part of God. Because of what Adam did, we inherit something naturally corrupt. Not that God decides to create every individual as fallen, but as a natural consequence of the fall. So since man no longer enjoys that direct fellowship, the consequence is (partly) that his own ways are before his face and not God's. That is why God's presence so terrorized Israel :
And all the people saw the thunderings, and the lightnings, and the noise of the trumpet, and the mountain smoking: and when the people saw it, they removed, and stood afar off.
And they said unto Moses, Speak thou with us, and we will hear: but let not God speak with us, lest we die.
And Moses said unto the people, Fear not: for God is come to prove you, and that his fear may be before your faces, that ye sin not.
Exodus 20:18-20
Man cannot sin in God's presence (EDIT : I take this only from Exodus 20:20....but don't say it dogmatically - only that it seems like an awful state for the one who doesn't have the changed nature), but to the man who has not been changed, this is the way he is (will be) when in His presence. The thing is, because of the fall, this is a forced nearness. Man simply cannot dwell near God (implying walking in His ways) on his own. There is nothing in him to do so. But change the man (i.e. make him born again) and that new nature now loves what the natural man (as seen in Exodus 20) simply is unable to tolerate.
So God made Adam a certain way but we are not born in the same way Adam was created. We naturally are subject to the fall.