When I was in school (USA), any attempt to stand up to bullies was punished immediately. Administrators and teachers made it very clear in no uncertain terms that bringing problems to them would result in either punishment or apathy. Essentially, kids were stuck in a Catch-22 situation. I'm not surprised that the tradition continues today.
My children got the US equivalent of this, which apparently started in the wake of the Columbine shooting. It was garbage. None of my kids could figure out exactly how to stand up for their peers, no practice was ever included with the exhortations.
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.
I'm not sure about "upstanders" against bullying in and of itself, so much as a matter of extremes... for example, when there's physical abuse or fighting. When I was coming up, the lesson was, "If you have the ability to intercede, you have a responsibility to intercede."
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.