all Starship personnel wear the Starship emblem that we have established for our Enterprise Crew Members to wear.
Again, it's right there in the memo. Non-Starship personnel don't necessarily wear the same insignia, so starbase and comm station personnel wearing something else makes logical sense and is consistent with with we saw. Really, only Decker and the couple of guys in "The Omega Glory" are at odds with that. Finnegan was a cadet.
Now, as to why some starbase personnel
might wear the arrowhead, that's a different question.