I can only guess, but my guess that I think makes sense, is that the products that have the expired licenses were, themselves, licensing other elements to use as part of it. The agreement Adobe had with those 3rd parties (because the email said 3rd parties might take legal action, not Adobe) likely expired as it relates to those products and, therefore, continued use of unlicensed products opens the user up to problems with third parties who no longer give their permission for anyone to use their pieces of the puzzle.