Did anyone meet a person who'd never complained of life? There were no such persons ...
Why live painful, difficult? After all, God created us perfect ... but then why we were thrown to the lowest state? We have to suffer, there is blood on the ground more misery than joy ... Why man is doomed to suffer?
The Qur'an mentions the city and the people that were once destroyed. But there is one feature: all of these cities, and the people were prosperous. There is something to think about, is not it? The inhabitants of the cities and countries had fun, celebrated happy life, their wealth, prosperity, abundance of children and other benefits. Is not this man should aspire? But why, when society reaches such a life, it is destroyed again? Perhaps the reason for their destruction is that they have forgotten what is suffering?
Life forces to suffer because there is no other way for the growth and maturation. Suffering necessary because only suffering can make a person aware of the world around himself in it, and what awaits him at the end of his life. And when a person is happy and fun when everything in life is easy, a person becomes distracted. He loses his vigilance, he stops to think about the meaning of his stay here. He even stops to think about death, and if he thinks about it - it is only to think about the invention of pills of immortality. But the Prophet (peace be upon him) said: "It is enough, and death as a warner."
And if a person person does not think about death, he just does not remember about religion. So, there is no suffering - no reason to go to the temple. Indeed, Allah in the Qur'an repeatedly reproaches people for their short memory when it is bad - people call God, and when God saves them - they immediately forget about Him. Hence - the suffering turns people to God. Carefree life - move away from Him.
Finally, there is another reason for not surprising the abundance of suffering. It is simple: we're not in Paradise.