Sky burial or ritual dissection is (was once) a common funerary practice in Tibet wherein a human corpse is cut in specific locations and placed on a mountaintop, exposing it to the elements or the mahabhuta (the 4 great elements, Earth, Water, Fire, Air) and animals – especially to birds of prey. Most of Tibet is above the tree line, and the scarcity of timber makes cremation economically unfeasible. Additionally, subsurface interment is difficult since the active layer is not more than a few centimeters deep, with solid rock or permafrost beneath them.
Sky burial is considered an act of generosity on the part of the deceased, since the deceased and his/her surviving relatives are providing food to sustain living beings. Generosity and compassion for all beings are important virtues in Buddhism. Although some observers have suggested that Sky burial is also meant to unite the deceased person with the sky or sacred realm, this does not seem consistent with most of the knowledgeable commentary and eyewitness reports, which indicate that Tibetans believe that at this point life has completely left the body and the body contains nothing more than simple flesh.
*Some texts were paraphrased from Wikipedia.*
I personally think it just looks cruel because I'm not familiar with it. Although I thought it's important to know about it in order to understand the differences that come between religions.