It's an interesting question.

Email has morphed into something quite different from when it started, and was a good way for humans to send messages to each other. That use case has mostly been supplanted by SMS, whatsapp, the social media app of the day, etc.

These days, it's really only used for that purpose mainly inside organizations, and "public" email seems to be overwhelmingly marketing material and automated notifications, with only the sporadic message from a human being. It's kind of functioning as what people wanted RSS to be.

The cynic in me would say that it survives because it is an effective tool for marketing, and the subscriptions / recipients are controlled by the sender.