Mainly because I like to write, and people usually like my writings. So, why not ?
Also - because it is a good way of learning. When I was a student, I remember that my favorite reharsal technique was to pretend I was explaining the topic to an imaginary person that knew nothing about it - and that technique worked very well, because when explaining, I very frequently discovered flaws in my knowledge that prompted me to improve even more. Blogging has the same advantage - with the additional bonus that the readers are real, hence they will discover (and hopefully tell me) much more flaws than my good old imaginary friend. A flaw discovered today is an error avoided in production tomorrow.
Then there's interaction with others, that will for sure provide me with interesting insights and other topics to investigate, or even a full-blown discussion extending across posts, blog pages and even ... restaurant tables.
So, here I am. Hope that you will find this Oracle blog useful ...