Cannot "just" switch? What's that mean, exactly? Surely there is some kind of a procedure for people to change their "sports" nationality if they really have emigrated and so on?
(You might think of having a rule that you can only change your "sports" nationality if you "renounce" your previous citizenship, but it many cases it's not possible to "renounce" citizenship: you can let your passport expire, but whatever condition, such as place of birth, allowed you to apply for that passport in the first place would still exist so you would continue to have the option of receiving a passport for the previous country if you ever wanted to apply for one. Moreover, it would be impossible for you to prove you hadn't done that because countries do not, as a rule, issue documents to certify that a given person does not have a valid passport!)
(You might think of having a rule that you can only change your "sports" nationality if you "renounce" your previous citizenship, but it many cases it's not possible to "renounce" citizenship: you can let your passport expire, but whatever condition, such as place of birth, allowed you to apply for that passport in the first place would still exist so you would continue to have the option of receiving a passport for the previous country if you ever wanted to apply for one. Moreover, it would be impossible for you to prove you hadn't done that because countries do not, as a rule, issue documents to certify that a given person does not have a valid passport!)