Problem 1: If the person has already done work to refine their skill with rationality on their own, they may figure the blog is likely to be more of the same old stuff. LessWrong would love to have more of that type of person, don't you think? They're not going to be interested in the topic of rationality presented plainly all by itself. You have to immediately prove to them that the particular collection of information is fresh and exciting, or they slot you away in the "already read about it" category.

Problem 2: A random post isn't necessarily going to be a good post. I did random post several times before I found one that excited me and made me realize that LW is awesome, and the ONLY reason why I kept trying was because so many friends had referred me to LW that I was starting to think I was missing something.

Problem 3: A lot of users are busy and don't take their time with new sites. They usually will not read an entire front page. You have a few seconds to interest them. You either put something awesome in their face, or they're lost.