why in the evaluation menu and in other menus the table cannot be deleted?
No need to delete the table. You can simply select "Hide Rubric" option. This will make it invisible to public but available to you in case you need it later.
There are two input boxes in evaluation page. The rubric and content. If you make the rubric (table) hidden - it will not be available to public. Whatever you write in the content box will appear to public.
They can view online or you can export your webquest as a pdf document. The link for exporting to pdf is located in the bottom section of your webquest.