Because you now need to implement a full text search or even natural language processing to identify personal identities in your comment, and that’s quite challenging. An evil competitor could register several accounts, purposely leave those comments with personal identities of those accounts on the system and then request to remove one of the accounts.

Your algorithm needs to parse those comments, identify which Comments mentioned the to be removed identity, and remove them without breaking the integrity of your database. Failing to do that, you get sued...