Why does Pluto rejected from the planet category

 Why does Pluto rejected from the planet category 

There are mainly three criteria for a celestial body to be called a planet. The space body should orbit it's nearest sun, the shape of it should be approximately round and the orbit of the space body should be clear. Pluto full fills the first two criteria but it's orbit is not clear, it exists in the Kuiper belt (a belt consists of numerous asteroids and dwarf planets). So The International Astronomical Union rejected pluto from the category of planet. Pluto is now categorized within dwarf planets.