God did. He did become a man (Jesus) and fix them himself. God and Jesus and the Holy Spirit are all God.
Again, I'll rehash how this works. God of the bible created a system that didn't work from the start due to conditions that he put in place with foresight in mind that it WOULDN'T work (he is omniscient, right?). Then, when it didn't work, he killed everybody except one family. Then temporarily allowed incest in order to populate the world (for the second time at this point), then forbade it again. The system never changed, and things continued to suck. So, in order to create a loophole to get around the rules that he created because they didn't work, he sent himself to earth in the form of Jesus in order to ultimately get flogged and crucified and die in order to fulfill the need for blood sacrifice which he put in place. Essentially, he sacrificed himself to himself in order to pay for the condition (sin) that he created.
Once more, all he had to do was come back down and say "hey, uh, guys. Listen up. It's me, god. So, you know how I said you were all sinners and how blood was to be spilled for pretty much everything? Yeah, you don't have to do that. Listen, just be cool. Be awesome to each other. Ask for forgiveness and truly mean it and that's all you gotta do to make me happy. I kinda caused this whole big deal anyway".
If I, a mortal with admittedly limited intelligence, can come up with a better solution that would leave NO doubt in any person's mind whatsoever so that there is absolutely no confusion between any two people, then why couldn't a god? Maybe, just maybe, because a god didn't write it and the writer's realized "hey, this blood sacrifice thing is getting outta hand. We need to revise this so people have a bit more hope and so we can keep animals and virgins and people guilty of adultery and other crimes alive". They came up with a story, put it on paper, and voila. There you have it. That seems like a likely outcome. No, I do not know this as fact, but I do think it is pretty likely.