The difference is Bad Robot was hired to make those films. It's no different than contracting Gene Roddenberry's Norway Productions to make TMP. It's work for hire. There are rules about what happens if someone creates characters for an episode or a film, and said characters get reused in subsequent productions. It's why Paris was Paris and not Nick Lacarno on Voyager: you have to pay the writer every time you reuse a character they created (the rules are different for staff writers). It cuts into your profits to pay out to an outside writer, ergo, it's easier to just make up new characters. So, if you keep Garth, you'd have to pay the estates of the originating writer(s) for each segment Garth appears in. If you use the other Axanar characters, you still have to pay the writers who created them. So, why bother? Just make your own show without that baggage.
Great post. Thanks.