Why is Pluto no longer considered a planet?

In 2006, the International Astronomical Union (IAU) removed Pluto’s planetary status and designated it as a dwarf planet. It comes after defining the “Planet”. 

A celestial object must satisfy the following three conditions to get designated as a planet.

1. It must orbit the Sun.
2. It should be large enough to acquire an approximately near-spherical shape.
3. It has to clear its orbit, i.e. it has to exert its orbital dominance and clear the neighbourhood circling its orbit.

And Pluto has been removed from the list of planets since it did not satisfy the third condition as per the International Astronomical Union.