Problem: Bookmarks created in ArcMap do not import to a hosted web map in ArcGIS Online
Bookmarks created in a map document in ArcMap fail to display when the map is published in ArcGIS Online as a hosted web map.
This is a known limit.
Solution or Workaround
Re-create the bookmarks in the ArcGIS Online web map after the map is published.
See the link in the Related Information section below to learn how to create a new bookmark in ArcGIS Online.