In order to prevent my answer to be misunderstood/wrongly interpreted, let me state few thing now, at the beginning:
- I LOVE to play chess.
- I am inactive, and doubt I will ever play on tournaments again, but I still follow the game.
Now, let us proceed towards answering the OPs question:
...I know many people who stopped playing competitively after primary school but still follow the sport. Why is chess different: why do so many young people divorce themselves from chess completely when they feel they've reached their potential and can't advance any further?
In order for someone to continue sports/mountain climbing/collecting stamps/whatever they need to have a reason for doing it-and it must be a very good and strong one!
So let us start examining this from the athlete's point of view for a start, and then we shall compare our conclusions with those for a chess player.
ATHLETE"S POINT OF VIEW:
A child athlete could like sports because he can :
- Play with people of similar interest and of the approximate same age and he can be a part of something;
- He can improve his health or maintain its good shape, he could get popular which can give him many social benefits;
- He needs little work to do in order to improve compared to a chess player, and if he continues to pursue sports there is a chance for him to have great future ( fame, money and so on ).
CHESS PLAYER'S POINT OF VIEW:
Young chess player is surrounded with his peers at the beginning but as soon as he progresses he meets usually older people to play against. Imagine a child on a decent tournament ( this scenario is really plausible since 12 year old can reach FIDE master/near FIDE master strength ) surrounded with older people-it makes him feel awkward, like he does not belong there. He can not socialize with them since they have no common conversational topics due to age difference-which will lead to loneliness, unlike the athlete who is usually surrounded with its peers and feels great for being a part of the team, for belonging to a group.
Chess improves mental abilities ( some mathematical disciplines and memory ) , but spending too much time on the board neglects child's physical development. In that age physical development is far more important on the long run than to be a spelling champion. Furthermore, a successful athlete gets the social benefits like popularity in school and many others, while being a chess player is not being fully approved today-nobody likes to lose from a girl and guys are labeled as boring geeks. Sorry to say it, but in the long run being the athlete really has its benefits even if you do it for fun but playing chess in your free time does not.
- Regarding the improving method athlete again has it easier. Let us take basketball for an example: If a tall child and a short one start training and invest equal amount of work the taller one will still be a better player because of his innate height advantage. We see this in sports all the time-physical attributes play huge roll. In chess these two will be of equal strength if they invest equal amount of work. Why is this so important? In order to be the best in sports you need both physical attributes and skill yet in chess pure skill is the only thing that counts. Let us take Shaquille O'Neil as an example-his free throws are horrible, but he is still a top player because his physical attributes combined with other skills compensate. In chess, lack of skill can not be compensated-you must work hard to remove your shortcomings.
So what is the result for our 12 year old chess player? Work your but off to be good chess player for what-to be socially labeled by a bad stereotype? So you can get kyphosis/scoliosis for sitting on the board for too long? We all know that only few chess players ended up millionaires compared to countless athletes out there. So what is the future for a child if decides to really pursue chess? He will most probably reach grandmaster strength with hard work only to realize that there are many others like him and that he will have to work even harder just to have a chance to become top level GM. Strong memory and good mathematical abilities do not count much-we have computers/smart phones and other stuff to do that for us, yet physical fitness is still of paramount importance for us.
Also, you can find sports report on any news station/newspaper/Internet page, yet chess resources are very skimpy-again this requires hard work or maybe devotion is the true word and not many 12 year old children possess it.
To conclude: After playing chess for sometime child will reach the peak at strengthening its memorization skills and after that it decides to pursue other interests and to explore new things. Devoting oneself to one thing at this early age is something that is not seen very often-children at that age learn about the world around them and it is normal for them to want to try everything. To devote oneself to chess-and you really need to devote yourself based on the reasons posted above-requires strong characters.
I will end this quoting Mikhail Botvinnik:
"Chess is for strong people, of strong character."
How many children do you know that possess these admirable traits?
Hopefully this answer will shed some light on the matter.
Again, I do not mean anything insulting, I just state my oppinion which is backed up with arguments.
Fell free to comment, I will gladly reply.