Why do we write blogs

I am not an active blogger( not active in real life too). My very few blogs are a testament for that. I suddenly got a doubt regarding the purpose of blogging. Why do people write blogs??

1. To share information? Then whats the use of writing personal experiences ( Even i did it once)
2. To flaunt the communication skills ?People even refer dictionaries to write blog like I did for my first blog
3. For time pass? This can be true to a certain extent but why do lazy people push themselves to write blog ( There are various examples for this which again includes me)

Blogs can be categorized into three types
1. Technical blogs or in general, knowledge blogs.
2. Personal blogs
3. Abstract blogs

Technical blogs serve the actual purpose of blogging which is sharing of valuable information. But hardly 10% of the blogs will fall under this category.

I am still thinking of a purpose for a personal blog. Why do people have to pen down their personal experiences? Why should I read about X's trip to Ooty? Why should i know how X fared in his interview? If i am a person who is supposed to know all these things then is blog the right medium to know it? Won't a personal mail or a call suffice.

Then comes the most important of the three and the one which is ubiquitous, the abstract blogs whose sole purpose is to flaunt the vocabulary you have. The number of times the reader refers to online wordweb is directly proportional to the percentage of victory the writer gets. Again these kind of blogs at least serve the purpose of improving the reader's vocabulary.
But are the above mentioned reasons adequate or is there anything else which makes a person write a blog??

Above all the sense of accomplishment the person gets once he publishes the blog online instigate a person to write a blog. The pride he gets in displaying the link in his gmail status messages incites him to do so. The invaluable joy he feels when he sees that single comment after 3 days of refresh makes all his pain to write a blog die down to ashes.
Now why did I write this blog?
Which category will this fall under?
I am confused.