Actually, there are several reasons it got demoted, but chief among them is that it's one of the innermost members of a belt of similar icy bodies called the Kuiper Belt, which we estimate is about 50,000 members strong (better get naming!). It also hasn't really cleared its orbit, nor is it even close to orbiting in the plane of the rest of the solar system.
oh, so funny ^^ when they had said that pluto wasn't a planet anymore, i was like 'Hell no! I will always concider pluto as a planet. You can all just die for all i care' God, i love pluto so much, she has to be my fav scout of all time GO PLUTO!!!!