Quote Originally Posted by Finding_Fantasy
A larger women would probably lack the mobility and flexibility to accomplish such poses.
That's might as well be a producer issue: Larger women would required really strong premises, which means a higher cost.
Assume a simple sling.
For a light weight, most won't bother about the fixations.
With a heavier load, quality is mandatory; As quality usually doesn't come cheap...

Back to the original remark: It might just be a geographical issue.
Most US movie features thin and healthy people, even when that country has probably the highest rate of fat people. US bdsm movies are just like other US movie.
From personal experience, German bdsm movies can have larger women (along with real sex act, which US ones do not by law, I believe).
Larger women in these movies could be top or bottom.
Weight does not mean amorphous: you need to move the cane right, even if you're a large top!