A few hundred people climb Everest every year and most of their trash stays where they toss it. Even experienced climbers are too exhausted after makng the ascent to do more than just climb down. After 50 years or so it adds up. From what I hear, the rubbish is mostly discarded gear, but there is a sizeable amount of organic debris, including, as someone mentioned upthread, a number of bodies.
True. In a relative sense Everest is easy to climb in comparison to K2 which is almost the same height but has no tourist type climbers.