Many people writing personal diaries/letters probably didn't do so with the intention of it being saved forever in a publicly available, easily searchable archive.

Yet such data is invaluable to historians and can give us a window in time through the eyes of people who lived that time. Having that publicly available data lost for all time would be an immense loss to future generations.

I'm sure in a few generations, some historians will study those archived porn blogs and get an insight on the evolution of humans' relations to sexuality that today's historians can only dream of.