Not sure what’s the chicken and what’s the egg here but maybe they didn’t know how much work would have to be done and thus how much money it would cost.

But it’s all just speculation and neither am I trying to defend them nor do I have a use case for this particular feature. I just wanted to interject a different possible scenario.

Well maybe they found them and they told him what he’s saying now?

It’s not solely about the emails you send but the emails you receive.

If your email provider is google for example then all the emails you receive, like shopping, newsletters, whatever are used to create an advertising profile of you. That is one of the few things you have and should take control of with a privacy respecting provider.