Whenever I read a carefully composed English text with a pun in it, the said pun is always followed by an information whether or not it was intended.

Why is that?

Where I come from (the Czech Republic) it is considered harmful to the humor to explicitly draw attention to it or, worse, explain it. But in English, as it seems, you can't play with the language with impunity (pun intended very intensively). Is it just a matter of correctness, or is there something else behind it?