I can totally see how you would choose to go that route. Imagine you're an immortal soul and you know it, and you know nothing can ever harm you, really. Then each Earth life is just like a movie, of sorts, in which you are the director, the playwright, the main character, etc. If you're in that place "between lives" and look "down" on Earth, I bet you find all that petty drama going on here pretty amusing.

And then you get reincarnated and forget. And when you're in the midst of that drama, it sure doesn't seem all that funny anymore, especially since you don't remember that you're an immortal soul and don't have that big-picture view anymore.

You can get it back, though. With practice, you can actually learn to see yourself and your life with some degree of detachment, and it's incredibly instructional, I can tell you that.

So, to answer your question: Why would someone pick parents that abuse him? To overcome, simply. Traumatic experiences can break you or they can be extremely character building. Ask some of the people who had really hard childhoods and are now on top of their game... they'll all tell you that, had they not gone through what they did, they wouldn't be where they are today. Goes for me too; I had some real crap happen to me as a child and teenager, but it ultimately made me stronger.