The thing is, most people don't care about privacy. Even if the person knows about the broader privacy issue, he/she may not care. It's all about convenience and dopamine hit in the modern digitised world.
Also, the most privacy-respecting emails has less brand name recognition. Most people are accustomed to Gmail, Outlook and Yahoo. If they see Tuta as the email address, most people would think it's odd and maybe even fake. In an industry where reputation and name recognition is important, especially in legal, Tuta would sound suspicious. I know I would feel the same if I weren't familiar with Tuta and the lawyers uses Tuta. I know there is Proton, which has a more marketable name, but the CEO is a fascist-loving Trumper so it's not any better for privacy in the future.