Users are unable to delete items such as web maps, tile packages, hosted feature services, and tiled map services in ArcGIS Online.
This issue may occur when the Delete Protection option is enabled for each of the items in ArcGIS Online.
Note: Esri introduced Delete Protection in the ArcGIS Online December 2013 update. Delete Protection is enabled to prevent items from accidentally being removed from the site.
Before deleting items, disable the Delete Protection option for each item. For more information, refer to the following blog post, Prevent Accidental Deletion of Items from ArcGIS Online.