Why monetize a Site or Blog?

I been to some sites which has plenty of visitors, I wonder why the owner did not monetize it? In fact, monetizing can make them earn money online.  What a waste.

Anyway, how do you monetize your site or blog? Its actually very easy, you just need to register to a monetizing site or company. The one i'm using now is my sister account in Google Adsense.

Joining in adsense network was made me earn little because I only have few numbers visitors but I think  I will soon reach the set payout which is $100. Aside from adsense there a lot of monetising site out there. Just like the following:

Adgitize This is another monetizing site that offers wide variety of earning opportunity and pay through AlertPay. visit the site for more details.

Adbrite This is another one and also offer revenue earning and pays trough Check. Visit the site for more details.