As for why this world sucks, I've heard that it's because of free will. Supposedly by God allowing all the evil and misery of this world to even happen in the first place, it allows free will to be a thing somehow? One may wonder why God did not design existence differently so there is not so much suffering -- but free will is a thing still.
Then of course there's the traditional Christian idea that this world sucks because of some fruit and a talking serpent with legs.
There is also that Gnostic belief that this world is the creation of an evil lesser god, so he can feed off of the misery of those trapped within. In such a very grim view, that tunnel seen in the typical Western "near death experience" is a kind of "soul trap", designed to trick souls into "reincarnating" to feed such an evil god more misery. With the Gnostic view, one may wonder why the true God (beyond this natural existence) even allowed such lesser evil god to exist and make the sucky world in the 1st place.