If there is a God, why doesn't he stop cancer, or blindness, or natural disasters etc?

If there is a God, it should stand to reason that there's an afterlife where dead people spend eternity. Therefore stopping death would be counter productive, and stopping an early death would just slightly reduce our already pathetically insignificant period of time in a place which really isn't that good anyway. As for anything related to suffering, any differences between even great happiness and sadness on Earth would be negligible compared to Heaven and Hell. They'd both be pretty much neutral.