I can see why they don't allow photographers into the Lower Antelope Canyon. It's much narrower than the upper canyon and tripods would block passage for others. When I went in 2008, I drove up to the Lower Canyon, paid my $20, was shown the way down and was allowed to wander through the canyon for 4 hours on my own photographing to my hearts content. I saw 2 other people in the canyon, one was a photographer.
Popularity of the canyons has since exploded and tripod wielding photographers just would take up too much room in the narrow canyon.