Why do people suffer according to Hinduism?

There is this concept called as life after death. The current life you're living is not the only one you've had. This might be your hundred billionth life. Now, in every life you do some good deeds and bad deeds. [The 'deed' issue would be explained later]. Now when you do a good deed it is saved in your own body. This goes on as u live on. Now when you die, nature checks the ratio of good deeds to bad deeds and when the ratio reaches a certain value, you're given a human's life. Other wise you're given the life of anything else.

Now if the ratio is very good, then you get a good human's life else you get a bad human's life. Now the question arises, why do we always favour man's life? ... Just because he is the most intelligent animal? ... No! ... the answer is... this cycle of life after death.. life after death.. one after the other is very tiring and never ending. There's only one solution to end it and become free. That solution could be found only by man. There are many solutions like meditation, naamasmaran, vipassanna, etc. But, to practise this, we need a subconscious mind and a conscious mind which only man has! and a superb level of intelligence which again only man has. Thus, a human's life is gifted to us by nature to become free of this viscious cycle of life and death, happiness and sadness, love and hatred, sufferings, distractions!

I hope I've answered your question. I've made it too short though!