The reason I use tutamota (similar to protonmail) is to stop the Googles and Yahoos and hotmails from scanning all of my emails, using them to advertise to me, selling the information to advertisers. Could you imagine if the US post office opened up all your mail, read it, and sold this information to anyone who asked? Preposterous. And keep track and sell who you send stuff to and who you receive info from? Of course, if the government decided to monitor you regular mail, they could. Fine. Nothing anyone can do about that. But at least the USPS doesn't read everything you send and sell that info to commercial entities.
So, that is why I use those types of services. I don't want to be anywhere near Googlemail, or Yahoomail, or Hotmail, etc.