By the time my son was in elementary school, it had become, "Don't get involved, get a teacher or call the police."
I think when it comes to non-violent bullying, that people should encourage and empower the bullied to stick up for themselves... and should it become violent, then intercede as necessary.
Sone armchair psychology here, but this doesn't seem surprising to me:
One thing a bully needs is to feel strong and secure in their peer group: They feel they can get away with bullying the victim - or even gaining validation - because they believe the majority of the other students are "on their side" and the victim is socially isolated.
If a number of students stand up and call out the bully on their own, they signal to the bully that this is not the case - and that the bully might risk social isolation if they continue.
But if everyone just got an official lesson before to stand up to bullies, this signal falls flat - because it's obvious the students are just "acting on orders" of the school authorities and this is not their real opinion. So the bully might believe they're still "really" siding with them, no matter what they say openly.
For my part, it looked the teachers and administrators offloading the work to students. "Only you can prevent bullying" looks like "I, as a teacher, am not going to bother doing it".
This made me reflect on my own school experience and I've come to believe that some schools and some teachers tolerated bullying because the bullies were doing discipline for the teachers. Maybe not excellent discipline, but it was easy. I also believe some teachers allowed bullying to punish kids they didn't like for whatever reason, nonconformists, smartasses, or minority group. Bullies gave PE teachers plausible deniability.