It's delayed because the employee fears further retribution still. You need some distance between yourself and the bloodthirsty dog before you can even hope to reduce your productivity, or you'll be mauled quite enthusiastically. By delaying it for days or weeks, by being out of sight when it happens, there is plausible deniability that can let them survive the attacks.

Managers do this to themselves, they punish people who would give them the quick feedback loop.