As a marketer who sometimes needs more control over the look and feel of my emails, I would like to have access to the <head> block in email so I can place <style> tags and today that isn't possible even in the content editors that provide access to the source code (HTML editor, WYSIWYG).
As an example of where I need access to the head tag for my style tags. Gmail needs a specific format of styling to display an email in 'dark mode', and because gmail will automatically modify style tags in the <body>, access to the <head> is required to enforce the dark mode:
https://www.hteumeuleu.com/2021/fixing-gmail-dark-mode-css-blend-modes/