why to the pigs want everything to them self ?

The Pigs are a metaphor of the elite who want everything regardless of political ideology. Although the Pigs represent Stalin and his cronies, they could represent any system that has been corrupted. THe Pigs, Napoleon in particular, want power and all the trappings that go with it. Old Major had an egalitarian vision but like most moral visions, it gets corrupted by greed and power.