First of all because it is a lot of fun!
It is great for keeping an online diary and write about your experiences in day-to-day life. You could write about the development of your children for example and the fun and chaotic things that happen every day.
You will meet and connect with many other like-minded people online. Although they may never replace your real-life friends they could well become a strong community for you that will give you a lot of support!
It is a a great way to develop or build on a passion that you have. You may want to share your skills with people around the world or just share ideas with others that have the same passion as you.
Finally, it can become a great way to earn a living. Imagine working at a time that suits you! No more commuting and being completely in control of your own time and business.
That is what blogging is now for me. It’s my full time business and I’m doing what I love.