The way I see it, we were created (not directly, but way back when life was created/developed to where we are today), to live in our world as we chose. Those who want/need God's help pray, and those who don't, don't. God doesn't cause earthquakes, or tsunamis, or genocides. Humans do. If one person prayed for another do die and that other one prayed to live, who would get consideration?
We are left do act as we choose. When cancer, aids, disease strikes, we are just humans. We can't expect to be immortal/immune to anything. Everything in nature is vulnerable to one or another, and it is not God's responsibility to make sure we all live forever and fulfill our dreams. He is there to help us, not to do it for us.
For suicide, the suicidal person chooses to take their own life. Would it really be better for God to save them? For one to kill themselves, they must truly be upset at their life, and for God to have them live through it would be terribly painful. God gave us an amazing gift in that we get to choose what we do with our lives.
It's not like everyday God decides a certain number of people get to live and a certain number have to die. We are humans, nothing more.