Why do innocent people have to suffer?

And:
Why do bad things happen to good people?

Reason 1: Chaos
As the good folks before me have explained, our world is chaos. Chaos is, after all, necessary because its the power that creates things. On the other hand, there's order. You need order to stabilize the things chaos has created.

Reason 2: "NO" is an unknown word
The Law of Attraction says, basically, what you think will happen. And "thinking" is not wishing, but "thinking" means crystal-clear, focused mental effort. "Thought" means "Will" here. Whenever you think about something, you send a signal out into God's universe: "Hey, here I am, and I want to have something!". Like attracts Like is a subset of the Law of Attraction. The problem is, your subconsciousness does not know the word "NOT". Don't believe it? Well, then please don't think about a green gorilla now. Got it? Then let's go on.

Your subconsciousness is the seat of your personal power. In your subconscious mind, you carry your opinions, prejudices, fears and hopes. It's your subconscious mind that sends out the thoughts your conscious mind has formed. But remember, your subconscious mind doesn't know the little word "NO". So, if you think "I don't want this to happen to me", what you're basically telling your subconsciousness is: "I do want this to happen to me". Green Gorilla, remember. So, the process of thinking boils down to this: Whenever you think about something, be it GOOD or BAD, you'll attract it towards you. So better be careful what you wish for.