When you add people to your event, you pre-create an account for them (unless they already have one).
People who did not have an account before, have a pre-created and pre-completed account thanks to the information given during their registration.
However, people who already have an account must accept (or decline) new informations that were associated with their account when you added them to the event. We call this a "mask".
Since the user has the last word on his profile, he is the one who has control over the modification of his information.
Also, if the user adds or modifies information on his profile, it will not be reflected on the organizer interface for reasons of privacy and data protection.