Just like with police. A minority of bad cops give all cops a bad name.

Except motorcyclists aren't an inherent part of a purposely oppressive system that routinely does horrific things as a core part of its working.

If a motorcyclist calls another out for bad behavior they don't (usually) have to risk their life and livelihood to do so.

ACAB comes from the idea that it's not possible to remain in that group as a subjectively good person.

I get it, you hate motorcyclists, possibly for good reason but the idea that a genuine equivalence exists between them and police is absurd.