because is considered a sport by organizations like the International Olympic Committee and FIDE because it involves structured competition, skill, strategy, and formal rules. for this reason the chess not is a sport.
Why is chess not a sport

Because sitting at a table moving pieces, competitively or not, isn't a sport.
It is recognized as one, though. But it shouldn't be.
It depends on how you define the word 'sport', of course. Does it require a physical element? The International Olympic Committee doesn't think so. They've classifed chess as a sport, though it has not yet won approval to be part of any planned Olympic event. And I just read that over 100 countries recognize it as a sport, including the United States, China and Russia... most of the other 95 countries have never annonced a position either way, and a few do not view it as a sport, including Great Britain, which sees it as a "game and a hobby" (and provides zero funding for chess federations).
For myself, I grew up thinking of sports as competitive activities that require physical exertion, physical skill, and physical stamina. So, even though I don't mind others considering it a sport, for me it doesn't quite fit the bill.
"When I use a word, it means precisely what I choose it to mean, neither more or less." - Alice in Wonderland (said by the Caterpillar).

Because sitting at a table moving pieces, competitively or not, isn't a sport.
It is recognized as one, though. But it shouldn't be.
*should be
*is a sport

A sport must meet these 3 criteria:
1) It must have a competitive element, and your competitor(s) must be human
2) Luck cannot be central to the sport
3) There must be muscle group training (excluding mental training) that will directly help you play better
3. is invalid. why? you said olympics, meanwhile Breakdancing:
It is recognized as a sport