I suspect a lot of people are no longer being taught these fundamental protocols by manual interaction with a terminal, since that's what SMTP seems to have bee

I suspect a lot of people are no longer being taught these fundamental protocols by manual interaction with a terminal, since that's what SMTP seems to have been originally intended for; and as someone who actually made use of that for a nontrivial amount of time, the "single dot on a line" to end a message has been permanently etched into my memory. Relatedly, escaping somehow seems to be a foreign concept for a lot of programmers, who wouldn't ever see the above situation and ask themselves "but what if I want to send an email with a line containing a single dot?" yet another large group of them finds it perfectly logical and easy to understand.