1) during the time, the climate in the North Atlantic was good and so living conditions were bearable. Mild snowless winters- great conditions for raising livestock. But the favorable climate quickly changed and life became too difficult for the Vikings to stay.
2) Diseases, plagues that have made its way westward on trading ships to Iceland and Greenland. A dwindling population may have reduced the Vikings' desires for travel and exploration. Fewer people made it impossible to continue supporting the isolated Vinland (one of the settlement) camp.
3)conflicts between Vikings and native people
4) long distant back-and-forth between Europe and North Atlantic was too much. Thus, they left north America and moved back to Europe (well...Scandinavia)