[partdavid]

There's actually a lot of things that embed a SMTP client for sending mail that should use a host MTA. The reason is that the user who actually wants to use "the thing" is often just about able to enter an SMTP server, but there's no way "the thing" can trust that a properly-configured sender MTA like sendmail is configured. Companies have huge fleets of servers that can't send system mail, and it's often not really under the control of the author of your frobulator program or the user, either. Mail itself is a specialist configuration, often requiring prerequisites in DNS, crypto stuff, policies, etc. It's "too much" for just being able to have your wallet or whatever send you mail; "contact your system administrator" is just often not a realistic option, in both large and small scales.

It's not a good reason, no--definitely not--but it's a real reason.

[leni536]

Use an SMTP library then.

[partdavid]

Agreed, for sure.

[kazinator]

The SMTP client needs to be configured. E.g. if there is a particular SMTP forwarding host that must be used, you have somehow get the "mail" utility to use that, and you must somehow any get any given SMTP library to also use it.