We don't know how much God does to alleviate suffering--I'm sure we'd be quite surprised if we did. And we hardly ever know why certain people are afflicted with particular maladies. Sin is going to strike people down, and people are going to suffer. I suppose God could go around cleaning up every minute result of man's sin, but He's told us exactly how He's going to solve the problem--separate the wheat from the chaff and burn the earth clean. In the meantime, God may choose to fully heal some and not others. I can only speculate as to why on a given circumstance. I know this: if we trust God, our afflictions will always have a purpose. It would be a shame for our suffering to be in vain.