COMPLETE_TRANSITION and SET_PARAMS are examples of actions that should not change the focused index for any router if they are applied to a child route.
The problem is that navigators can define their own actions that need to behave the same. For example, drawer actions (except maybe open drawer, unsure about that) need this behavior (or this happens: https://github.com/react-navigation/react-navigation/issues/5183) because they can fire on a child route when the parent stack (or whichever navigator) is navigating to another screen.
COMPLETE_TRANSITION and SET_PARAMS are examples of actions that should not change the focused index for any router if they are applied to a child route.
https://github.com/react-navigation/react-navigation-core/blob/master/src/routers/StackRouter.js#L574-L583
The problem is that navigators can define their own actions that need to behave the same. For example, drawer actions (except maybe open drawer, unsure about that) need this behavior (or this happens: https://github.com/react-navigation/react-navigation/issues/5183) because they can fire on a child route when the parent stack (or whichever navigator) is navigating to another screen.