Do you remember the ad campaign that said “You can’t xerox a xerox on a xerox”? This was created because Xerox feared its trademark was becoming generic. Xerox monitored its trademarks and helped to restore their value and legal status.
In trademark law, the trademark must NOT be a generic word. You cannot register “ball” as a trademark for a ball. It’s generic. There is no Beer-brand beer. Even to your eyes and ears, it is somewhat silly to say that. If a trademark turns into a generic word, then the owner loses all rights.
(And now, a boring legal citation on the topic. A mark is deemed to be abandoned when “any course of conduct of the owner, including acts of omission as well as commission, causes the mark to become the generic name for the goods or services on or in connection with which it is used or otherwise to lose its significance as a mark.” This is USC Section 1127.)