First, what is the definition of a blog? According to Wikipedia:
A blog (a truncation of “weblog”) is a discussion or informational website published on the World Wide Web consisting of discrete, often informal diary-style text entries (posts).
So why do I write posts?
The main reason I write and post on my personal site is for self documentation. Meaning I document processes, thoughts, ideas, things I learn and things I make for my future self. Over the years I have learned that by spending the time to document these things, it will pay big value to the future me.
If someone else can derive value from my site then that is an extra bonus and I truly hope that it helps them in a small way solve their own particular problem or challenge.