You shall certainly be tried and tested in your possessions and in your personal selves. (3:186)
Do men think that they will be left alone on saying “We believe” and that they will not be tested? (29:2)
Be sure We shall test you with something of fear and hunger, some loss in goods or lives or the fruits (of your toil); but give glad tidings to those who patiently persevere. (2:155)
Why suffering? Because of the Iblis/fruit of the tree affair. We (or at least, Adam) were not originally meant to suffer. But now we are tested for acceptance of the truth. After all, what is 70, 100, 900 years in comparison to eternity? A drop in an ocean! This is only a problem if you are looking at it from a "no life after death" perspective. Then a natural disaster is horrific, wiping out people from the slate of existence. But reality? After the death comes the resurrection. All in the blink of an eye. So does it really matter how you die when God is that which is responsible for existence/non-existence?
Also do you think natural disasters are "random"? I sincerely doubt they are. A lot of them are generally spottable (i.e. living near an active volcano, earthquake fault lines, etc). And we are given example after example in the quran of generations - when they reject the message and it is confirmed that they no longer deserve life, a natural "disaster" always wipes them out. To what extent is it really a disaster anyway - the parting of the sea and the drowning of pharaoh & co was a natural act. A disaster? Not in God's eyes!