Why do bloggers need Google AdSense?
Well to be able to answer that you first have to know how Google AdSense works. So in a nut shell. When an advertiser places an ad using Google AdWords, Google takes those ads and places them on the websites and blogs that have the most relevant content for that persons ad, and that have been approved for the Google AdSense Program of course, then that advertiser pays Google when someone clicks on their ads. For example, if you blog about bicycles, you will most likely see ads from bicycle manufacturers and possibly retailers on that page. When someone visiting your blog clicks on those ads, the advertiser who placed the ad pays Google and then Google pays you a percentage of what they just made from that click. Of course, the advertiser is hoping that the person that clicked on the ad will actually purchase the bike or whatever it is that they’re offering.
Keep in mind, Google is very strict about the integrity of this process. You are forbidden to click on any of your own ads. If you do, this is called click fraud and your AdSense account will be terminated and you'll probably never get it back. Google strictly prohibits you from asking others to click on your AdSense ads as well. It makes a lot sense too if you think about it. Why would any advertiser in their right mind want to pay Google just so your friends and family could click on your AdSense ads when nobody clicking is actually interested in purchasing the bike or whatever else the ad might have to offer.
The good news is that there's no need for you to try and cheat. You can make more money with your blog and Google AdSense just following their rules. All you have to do is write or blog about something interesting and unique, which is what the search engines want, and you'll have the right people reading your blog to and if they're interested click on the AdSense ads.
So good luck with Google AdSense and your blog.