Clearly who ever developed this feature, was not married, did not have children, and never went through a divorce...

Joke asside, this type of development approach is quite common, for example in my kids school app, both me and my partner are registered in the app for our two kids, when the school sends a message, both of us will receive a copy.

However, when one of us sends a message to the school, the other half only receives a copy of the original message, if the school replies back.