Why doesn't this feature exist? A possible reason:

I worked at a company which had baked their own ticketing system and implemented a similar CC feature. As a result of numerous issues, such as; being blacklisted multiple times, infinite looping due to automated ticket updating from email triggers, distribution list fun, out-of-office reply cycling, etc... we had to put extremely tight restrictions on automated emails. There were only a hand full of people in the company who were allowed to make changes to these lists and there needed to be a detailed communication between the email admins before we would allow this.

Basically, this is extremely difficult to do correctly and changes on either side can have far reaching effects to everyone involved.