It might need be something else, since we don’t force account names to be unique. Since you save the address in contacts and it’s given an appropriate name, not being friend to type out is not much an issue. At least from what I remember, the email addresses of all the other services I’ve seen are not easy to hard, e.g. "firstname.lastname@example.org".
A secondary reason might be to avoid being spammed. We often receive emails that are sent to random addresses @dynalist.io, like email@example.com and firstname.lastname@example.org, you might see trash end up in your inbox. Unless we set up a rule where you can only capture via certain email addresses (i.e. only sending from email@example.com to firstname.lastname@example.org would count), it’s hard to avoid this situation, unless we make the email address hard to guess.