Here is another nudge: how easily can you write a rule to delete from gmail inbox after say X days? (same question for outlook.com, icloud.com etc)
There are ways for technical users, but it nudges users to leave all the juicy data to the company, which can then use it in any way it feels (including monetization)
I dare say that I don't expect automatic deletion of emails from your inbox is not a feature many users are clamoring for, whether they have privacy concerns or not. Hence I don't think the lack of it is for monetization puposes or the lack.
If you are a business customer you can set an email retention period for your domain (under the 'Compliance' section) which deletes all emails and chat messages after N days.
There's a new "confidential" toggle on the web Gmail (at least for gapps accounts) that let newly composed email expire after a certain amount of time. Not available on Android Gmail yet. Just saw it yesterday.
The actual email to non-gmail addresses is just a link to fetch the mail body, which can be validated with SMS.
There are ways for technical users, but it nudges users to leave all the juicy data to the company, which can then use it in any way it feels (including monetization)