I agree with you, email header inspection for most, may be uninteresting. However...
(1) eMail headers can be looked at by the mail program, and using very simple matching domain sources, used to flag suspicious emails from non-suspicious emails. Also, if you are interested, you can view the original purported source of the email - though more than likely, its a VPN or broken Mail Server... Mail headers are a useful feature for those who wish to view them. However in the main, most ignore them.
(2) Likewise, mail content - which is invariably monitored, can be parsed for suspicious links. Microsoft has done a great job over recent years in filtering suspicious emails, though still some slip through their net.
(3) Attachments - generally don't apply to the iPhone (hence I am not considering here in my request)
Handling 1 & 2, together would cut down a lot of the issues effecting unsuspecting people. Or even, an amendment to #2 which checked the link being clicked upon, with the text in the email, and alerted the user... (no brainer... )
So, why isn't it being done ?
The monies obtained from these activities go to where ?