Long tail optimization also known as "ecommerce optimization" or "catalog SEO", is a term to mean ensure the proper naming structure, meta-tagging and labeling of every product found within the ecommerce site.
There are reasons why a site cannot make it to long tail optimization and they are as follows:
• The site is static
• The Content Management System (CMS) doesn't allow for meta tag coding
• The SiteMaster isn't aware that they can impact all the products
• Red Tape
Note: I know the article is too short to be included but I m sorry could not find more information on the same, so have to be content with the word limit.