Only because there are so many scum with no manners posting videos without the permission of the videoed.
I said scum.
I don't agree with you calling those people "scum."
I recently went to watch one day of a seminar at my dojo. I saw that someone from my dojo was recording the seminar. I took some pictures and video of the seminar, and posted a few 30 second clips of the instructor teaching on youtube. I never asked permission, and it never even crossed my mind that I was doing anything even remotely objectionable. I got a talking to from my sensei soon thereafter who stumbled upon the videos I posted (my youtube account name uses my initials
Apparently, the instructor requests that all recorded video be for personal use only, ie, I can just look at it to learn for myself, but I can't post it on youtube for the world. My sensei asked the other person recording the seminar to record it for his own personal use.
Of course, I immediately removed the videos and very sincerely sent an apology e-mail to the seminar instructor, but at the time I didn't think I was doing anything wrong. Being a teenager now, I've essentially grown up with youtube and the like. It seemed quite natural to me to want to share the cool videos I had of the guest instructor! Anyway, that's the last time I'll do that without permission. It was pretty embarassing!