1. Blogger is free
If it wasn't free, I probably wouldn't bother!
2. Blogger is simple
The fact that it is easy and quick to add a post makes it that much more attractive.
3. Blogging is enjoyable
Communicating (to however a small an audience) is enjoyable, and being able to design new posts fills a creative need.
4. Allows me to collect and communicate random thoughts
Like a journal, blogging has therapeutic value.
5. I can collate information from other blogs and websites
The more information I post here, the less likely I am to forget it or lose it.