In Japan, talking on the phone is prohibited in the train.
Actually, it does not have a definite reason. But you know, talking with someone else in person is ok. So, I have to say “It is just a rule.”
Come to think of it, that is so strange. Why is there such a rule? Since when has this rule been decided? All Japanese are not able to provide a reliable answer. They say “The rule has been there for ages.”
This is similar with ‘Which came first, the chicken or the egg?’
This may be the reason why Japanese say: “Sorry, it is the rules of nature.”