Could Blizzard fix it in a way that banned the gold advertiser cheats? Probably. Would it stop everything? … no. Some amateurs would still pilot their bodies manually to create curse words or other inappropriate language.
Is it worth the dev time for Blizzard to try to come up with a more complex fix when they already have a fix that works all the time? Nope!
Is it worth changing a feature in a fan service product thats entire point is to replay the game as it was 15 years ago, which means avoiding changes as much as possible. no.
Is it worth the dev time to change the way things operated instead of leaving it as is, because the off chance little timmy gets his feelings hurt? Apparantly yes.