Why so many ADs!

After several days off bloggerparty, I appeared. I cost some time to look through some text, there are lots of AD in it. Most of them are means to help make money. I was puzzled by them.
Do they really make money ? Have anybody ever made money by these means?
In china there also exist some likely AD, if someone registered ,then the recommender can get some income ,but vey little .
I think they are all junk !