Just a thought -- while it may be your umpteenth incident of encountering an unannounced cross-posting, it could well be the OP's first time even seeking help, much less seeking it in more than one place.

While it does make a sort of sense now that I've been exposed to it, there is no way I could have ever predicted that cross-posting without announcing such was considered rude; I learned that here from comments folks made in response to that activity by others.

It may make sense, but it is not obvious to everyone; and newcomers in particular seem most likely to be the ones who won't know.