No one ever reported that by the way. With their massive user base it would have already happened at least once especially in the light of all of these scandals of lack of platform neutrality.
What are you talking about? People constantly report their Google accounts being banned, very often for things they did in their emails. It seems impossible to me that you've never heard of someone being banned by Google because of something they sent with their Gmail account. Usually Google reports it as an unspecified ToS violation, but that doesn't mean it wasn't related to things they did in "private" correspondence via email.
I believe it has been many years since any Google employee has looked into a Gmail accounts message contents without prior permission from the account holder.
Twitter, Facebook, YouTube but never Gmail.