Money can be made doing blogs, and some companies will pay well established bloggers money to advertise their products. But anybody writing blogs must do it because they enjoy it, and are writing about something they love and are passionate about. The money side may or may not come, but if you are having fun, does it really matter?
For those that do want to make money doing it, first read "Crush It" by Gary Vaynerchuk, then check out websites like payperpost.com and a variety of different "ad" programs.