Why do bikers always seem to get hit from behind by and from other bikers, always?

Most of the accidents I've seen on youtube.com and other sites involves bikers getting hit by their biker buddies/riding partners.

Maybe it's safer to ride alone.

 

...or at least with people you really trust. I'm done riding with guys that are reckless. Too dangerous.

 

I only have two people that I'm really comfortable riding with... my dad and my high school friend. I can't stand it when my other buddies ride with me because they not only follow too close but I've had instances of them coming on my side during entry into a corner taking away my line. My dad and my HS bud ride at my pace so we stay together but at a safe distance from one another.