Sometimes, the idea of what a trope is actually about gets lost somewhere along the way. Either new entries miss the point somehow, or the author just read the trope title and thought they got the gist of it. This includes things like describing just anything remotely scary as Nightmare Fuel, when Nightmare Fuel was originally intended to be things you found unintentionally scary as a kid (hence why Accidental Nightmare Fuel was created and Nightmare Fuel repurposed). Remember though, that Tropes Are Flexible—what you think is decay may just be unusual usage on second glance.
Tropes Are Tools applies even here, however; Trope Decay can sometimes be the result of the TV Tropes Hive Mind correcting a problem. This is particularly true when the original definition is excessively specific or the trope experiences Missing Supertrope Syndrome. For an excellent example of both, witness the evolution of the trope Body Horror. Body Horror was originally defined as a narrow set of Virus Victim Symptoms. Over the course of several years, however, the commonly accepted usage gradually drifted and expanded to become Exactly What It Says on the Tin: the previously missing supertrope to all anatomy-related horror tropes. When brought into the repair shop, this "misused" form of the trope was voted by a significant margin to be the better definition and made official. The original narrow definition, meanwhile, is now the Traumatic Transformation internal subtrope of Body Horror's subtrope Transformation Horror.