My guess is because in the US, the municipality usually does not own the power-line or pole, and in the instances the municipality does own its electrical lines

My guess is because in the US, the municipality usually does not own the power-line or pole, and in the instances the municipality does own its electrical lines and poles, it has probably already deployed fiber. Also, having the fiber mounted lower on the pole means one can repair one or the other in isolation. The FB method seems like it could be dangerous for repairs, but I would like to see it applied in real life, too. So, legal and liability issues.