There should always be some type of bending loss in a fiber
optic cable, whether it's a SMF or MMF cable. The reason for a bend
loss being higher in SMF than MMF is that the core diameter of a
SMF fiber can be significantly smaller than the core diameter of a
MMF fiber, thus more of the light traveling down the SMF cable will
hit the cladding at angles above the TIR angle, and more power will
be lost.