The majority of my blog posts are not specific to the day I write them. They bubble out of thoughts, concepts, and a conglomerate of memories, readings, and stories. If I wrote something depressing, I don't only feel that way on that day or at that time. If I write something about an event, the event may have happened years ago. Upon reflection, most likely while driving my car or in the shower, I decided to share that event (or series of events) with some commentary relating to the framework of a larger topic. I write some draft thoughts down, write some of the blog and finish it later (sometimes much later), or I only write the title. It has even been a year before I revisited an initial post draft.
This is also why sometimes there are 3 posts all in one day. It just...happens.