Why are most of the modern 'thrillers' trash?

I picked up a thriller(supposedly one of the 'best sellers') from my lending library, flipped to a random page and scanned. What i read made my sick. The entire page was about gruesome torture, lies, deceit.. i flicked over to another page and found more of the same stuff.. What is happening here? Why have ppl developed a taste for torture and melancholy? Dont ppl like good sunny humorous books - leave the humour , at least books which have a sunny atmosphere? This reminded of Smith`s lines in the movie 'Matrix' .. "Man does not feel complete without misery.."