One part "it's been done that way since LJ added the concept of the friends page and it's not worth changing", one part "not wanting to give people a false sense of security by implying the contents of their reading page are private", one part "in about half the ways people use the site, public reading pages are an advantage in that they help people discover other nifty accounts they might not be following or allow people to build public reading lists to share with others", one part "because DW has the concept of locked/private entries, people don't have to rely on the concept of 'public but less discoverable' that they do on other sites", really.