Perhaps because many people, like me, have a primary non gmail address that is forwarded to my gmail address. That, and businesses with custom domains that use Google apps and thus have gmail as the UI.
Even if they say they don’t, how could you ever know they aren’t scanning business accounts? What in Google’s history has given you confidence in this conclusion?
Google has been found to lie and play dirty over and over again throughout their existence. You'd be a fool to think they don't even scan it. For "safety reasons", and oops, the contents of your email have accidentally been logged and stored, what a shame.
The source is Google (https://workspace.google.com/learn-more/security/security-wh...). Of course you can make the "they are lying" argument for anything, but in this case there would be several billion dollar lawsuits from every large company they signed a contract with if this was actually happening.
