[pmontra]

I could be wrong but it was not so easy to write to strangers until very recently. Except laws, books (with plenty of space to make the context clear) and journalism (same thing) I think that most written communication was letters to friends and relatives. Again, a lot of shared context. It's the internet (forums, comments on sites and social media) that lets us write to strangers maybe more often than we're writing to people we know.