[PatentlyDC123]

Your example seems a bit off. Yes, Coca-cola is not required to enforce their trademark via legal means; however, they may lose the ability to prove infringement of the mark later (even in another case) if they do not police use of the mark. I think there was also a case or course of legal thought by some judges that the mark's owner owed a duty (fiduciary maybe?) to actively protect the mark from infringement or risk losing the trademark rights altogether.