Because it's not a physical sport. Chess is included in the "Mind Olympiad" and the "Chess Olympiad".

Since 1950 the Chess Olympiad has happened every 2 years. The next Olympiad will take place in Istanbul in Autumn 2012.

no chess is not an olympic sport

*EDIT*

However there is a "Mind Olympiad" (games like Rubiks Cube and other Brain Teasers) of which chess is included. There is also a "Chess Olympiad".

The Chess Olympiad is a tournament hosted by FIDE every two years.

Its a tournament in which teams of 5 players from all over the globe compete against eachother.

Any chess association recognized by FIDE may enter a team of 5 players.

The last Chess Olympiad was played in Tromsø, Norway from 1-14 August 2014.

The next Chess Olympiad will be played in Baku, Azerbaijan. Also from the 1st till the 14th of August.

Who Knew - 2010 Chess Olympiad 2-39 was released on:

USA: 24 September 2010