I wonder if they avoid this specifically because it would make it immediately obvious how much they are able to scan, rather than ad targeting, which just gives

I wonder if they avoid this specifically because it would make it immediately obvious how much they are able to scan, rather than ad targeting, which just gives a vague sense that they know everything but not in sharp focus like that. I personally care far less about what Google can see than about what I might accidentally send, it hasn't happened to me, but it could be bad to send a work email to a random person, someone could even be fired if there was a trade secret. But I can see it upsetting more privacy minded consumers if it wasn't done very carefully, with a big annoying "This was generated in your browser and we do not scan message content" notice.