Etymologically, 'may/might' are linked to the idea of 'power', 'Macht' in German.
So asking for permission is ackowledging that someone has power over you.
That is why in our present world, which prides itself on having become more egalitarian than ever before, people prefer not to use 'may/might' when they are asking permission. It is felt as humbling – if not humiliating – oneself.
Instead, 'can/could', which come from the idea of 'know-how', 'kennen' in German, are used.
"Can I go to the bathroom?" is asking whether the objective conditions for my going to the bathroom are met… which is a bit blunt! The listener has been stripped of his or her authority almost entirely.
Putting 'can'in the conditional – "Could I go to the bathroom?" – does the trick of preserving both the speaker and the listener's dignity (*dignities?).
So, saying something 'may/might happen/have happened', dates back to a – religious – time when an ultimate authority granting or refusing permission for an event to happen was ackowledged: God's.
The uncertainty of the future was still felt as being to do with permission, hence the same modal auxiliary.
Se non è vero, (è ben trovato)!