Posts in wide-open social media like a blog go to everybody, regardless of their relationships. Church friends and drinking buddies get the same blend of pieties and dirty jokes.
The expected readership for my little blog here is myself, a few friends who use RSS, and search engines. Those are incredibly dissimilar. Search engines will be used by work connections, and I need to use the same formalities as in a meeting. Friends who use RSS will be interested in technology. Between me and myself I am interested in my internal monologue.
Yet on a day to day basis nobody reads this but me, so my internal monologue is all that matters. There’s a mismatch when it comes to search engines and friends who use RSS. It’s a form of context collapse.