This is often brought up and almost never true. No reasonable court would dump their trademark over this. It needs to be overwhelmingly out of their hands and in the public conscious. "Frisbee" for example still holds their trademark over the word Frisbee despite the fact that the vast majority of people don't even realize that it's a trademarked term. Businesses have de facto no obligation to defend their trademark to the extent that the internet often thinks they do.