Hi Erika,
The publish button won't appear for SD files if there is a reason that you can't publish from the particular SD file. Here are some possible scenarios to check for.
1. Do you have publishing privileges? If not, the publish button won't appear.
2. Does a feature service for this Item already exist? If so, the publish button won't appear on the item details page as it has already been published.
What is the workflow that you are currently following? Do you usually upload the sd files manually or publish from ArcMap or Pro?
Thanks,
Kelly