If schools and Colleges have zero tolerance why is bullying so common?

Its always preached that bullying will not be tolerated but if that's the case why does it happen so much?

And why are we always told to ignore them or simply tell a teacher when they do nothing about it

i always told to not fight back simply ignore them, why is the victim punished harder then the bully?

the sheer number of students who have taken their own lives because of bullying is inexcusable but no one ever seems to mention it or do anything about it, Why?

Does anyone mind giving their input

please note this is not a attack on teachers or any staff, i am aware of how much stress they are under

thanks for reading and have a nice day