Thanks for following up with me about this. I believe you must be looking in a different spot than I was trying to direct you to because "All eBay Sites" is not an option there.
Unless you have another default site selected, the "eBay Site" drop down menu on the lister page will default to "United States" (meaning eBay.com) and you would have to select a different option in order to post the item to another eBay site such as eBay UK.
If you are listing to eBay.com (US) or eBay UK, you would need to choose the “International Site Visibility” upgrade that is available in the Marketing Tools section to make the listings show up in the main search results on other eBay sites instead of at the bottom with most other international listings.
If you continue to have trouble finding this option, please file a support case and we will continue working with you on the issue through there. I'm really not quite sure where you might be seeing "All eBay Sites" displayed.