It's because there are a lot of really really really really really good players out there, that play with locked camera, but no ! 80 friggin percent of the people who give a (Christmas present) in the forums are all like "riot doesn't have to implement a mirror system ! Just unlock your camera, scrubbidy scrubby noob noob !"
And someone explained to me, that apparently because of there being so less of us locked players, the production cost of a mirror system wouldn't be worth the reward.
Tl;dr : If any locked camera player gets blue side, he will stomp you into the ground !