In some cases, it would be that the author forgets, but in other cases, it's a matter of time. If an author moves on to another story quite quickly, time taken to edit a previous story slows the progress of the new story. This is particularly true of long stories.
As for having them automatically submitted, I like to edit my stories a final time before submission, so it wouldn't work for me, but some authors might like having that as an option.
I think another factor in delaying submission is the confusion over what constitutes a sequel and what is essentially one story, although it might be written in two or more parts. My current story will have a sequel, therefore neither will get to the archive until both are finished.
Corrina.
