>find-function-search-for-symbol is a querying function. It can be used by different consumers, e.g. xref-location-marker.
>I'm not sure the user would want find-function-after-hook to run in every such case.
Right: the hook may be unnecessary called many times. Not good.

>Maybe help-variable-def's button definition's help-function should run the hook explicitly instead.
Thanks for the tip. This way looks more sensible.