Finishing a series or having a new author pick it up should be acceptable to us. It happens all the time in other forms of media, so what makes books so special?
Because buying a single book comes with the expectation that we are reading one person's story. Many books do not become series but, even if they do, we want to read the work of the person we enjoyed previously.
Comic books can't maintain that because of the long periods of time required to tell an ongoing story. A writer would have to stay on a book for decades to give us as much story time as we receive in even a single novel.
Comic book publishers also rotate their writers for any number of creative, marketing, and/or financial reasons. That doesn't happen on novels because the publisher must invest in a given writer to get the story they are trying to tell.
Personally I would prefer it if a comic book writer would remain on a title permanently. If Joss Whedon was still writing Astonishing X-Men I'd never miss an issue.
But novels and comics are two entirely different mediums despite featuring the printed word. They are entirely comparable any more than one can say that movies and television should be created in the exact same manner.