Because your mail will end up at Google anyway? Even if you don't use Gmail, all your friends do.

PGP solves that problem, and yours. Running your own MTA comes at a price. You need a domain, certificates, your ISP needs to not block port 25, possibility of abuse (so separate IP, server, domain, certificates), server which costs money needs to be maintained and draws power and requires space, and another responsibility to maintain. Disclaimer: It is possible containers mitigate some of the above problems. It is also a legacy protocol. Just run PGP on top of it and use any free provider out there. If you don't use that you can assume Google's oversight (the NSA) sees your mail.

I would like to agree with you (it sure is much easier than running a mail server), but isn't the problem that your friends also need to use PGP?

They are talking about MTA output. Mail input and archiving are still important factors.

I personally want to control my input addresses.

Hosting your own you can get funky wildcard postboxen.

Hosting your own you can archive all the mail without 3rd party approval.

I can see the advantage of the small amount of outbound being via someone else.

I have a VPS I use as a smart host.