Simply put, the reason is because God CANNOT violate our free-will, and most human suffering is caused by man to his fellow man in the form of physical, mental, verbal, or monetary and a whole host of other types of abuse. Of course there are then the big questions of; what about natural disasters, pestilence, famine and other forms of suffering not (apparently) caused by mankind?
The answer lies in the book of Genesis. It says in Genesis that when man decided he would rather be like God than be under God’s authority, not only was the body of Adman changed into a mortal one, but that the nature of the cosmos and the world was also changed with it. Along with the nature of all the plants, animals and even the atmosphere.
Remember when Jesus received his immortal body he walked straight through a wall on the natural earth we live on? This gives us some clue as to how it will be that in heaven we will not be befallen and subject to natural disasters and that in fact – we will be in command of the elements as Jesus displayed when he walked on water and performed a whole host of other miracles.
How could Jesus possibly walk on water you ask? Find out here; how Jesus could have Walked on water