The reason a user is not able to view all the Bulk Merge that has been sent out is because user doesn't have the Permission to do so. Note that the user needs to use the Administrator Role to be able to view the Bulk Merge sent by other users.
This is being addressed as an Enhancement under Issue: 131783 Permission > Please create a permission or restriction option that allows a role to be customized so it can view everyone's mail merge history.