Like Gloria pointed out privacy could be a reason of that. but in the first place, I don't really understand the situation if you would specify... 

In many cases, I think it's due to privacy reasons. In Japan, it is preferred that when taking a picture  you do not have other people who are unaware in the photo. This is because of privacy, and many would not like their face put online or other mediums. This goes especially for teens, since they are minors.
I'm not sure of the situation, but this may be a reason why.