How does Script Editor choose the applications to show on the 'tell current application' popup? How does Script Editor choose the applications to show on the 'tell current application' popup? For instance, why doesn't Preview appear on the list (see screencap below)? Is it possible to add applications to this list? If so, how?
Yes in Script Editor go to menu item Window → Library, then once you see this…



Just click on the + icon and there you can add any other apps you want.