WhatsApp is now testing the feature of not sending notifications to other users even when leaving a group.
So far, if any user of the WhatsApp group has left, a notification will go and if it is a group of your friend or relative, then you have to say why you have left the group.
To survive this hassle, WhatsApp is testing this new feature. The group admin will be notified when a group member leaves the group.
This feature is currently under testing and if there is a positive response from the users, this feature will be released.