Change in our language is slowed because we have high exposure to how the language was used decades, or generations, in the past. This exposure 'anchors' our language to a much greater extent than societies that do not have a high rate of written or audio records.
We acquire language in the form that it is used around us. In the absence of records, this means that the last generation's "slang" becomes our "normal speech," and whatever was spoken sixty years back is something we've never heard. This makes for a high rate of linguistic turnover, and four generations of separation will usually result in mutual incomprehensibility.
In modern times, I'm regularly being influenced by English that's 50 years old via Star Trek, Star Wars, the Beatles, the Rolling Stones, and Silver Surfer comic books. Because I still have exposure to generations-old versions of English, my speech will continue to resemble them.
We see minor evolutions in language these days - an extra word or changed usage to keep the dictionary-writers employed - but is there anything comparable to the differences you'd see across Britain in the 1600s?
[1] https://en.wikipedia.org/wiki/List_of_dialects_of_the_Englis...
I believe that we write more than we ever did. But what we write is not literature but a written form of casual conversation (blog comments, forum posts, IM, IRC, email...). It seems to me that it is likely, on the contrary, to favour a faster evolution of the language; especially for international English.