Because it never fails with some people
This was for demonstrating that the glasses function, not to show you that I think a 3-d movie will show up 3-d, through 3-d glasses that I recorded with my non 3-d camera phone haha.
You can clearly see the double images turn into one image showing that each side is sequential and only registering its needed part (NOT 3-D) at these times.. 0:40 and 2:10 Sorry!