Is there a particular reason this should be included?

I find it useful and many peaple do have the need to send mail from CLI.
...and among many alternatives, this is the simplest and the most flexible one (way better than ssmtp).

We already have mutt, which is a text-based mail client.

But that means having spool files in your directory and everything set up.
This is just a quick way of sending mail without the need to really set the account up for a user. I use it a lot for scripts and notifications, specially for the root account.