Quoting Stan Schroeder of Mashable:
The thing is, AdSense is just too easy to abuse. Click an ad, and there goes a couple of dollars. Turn it into a meme or a viral joke and thousands go down the drain, together with the entire idea of click-based ads.
I agree, the system is easy to abuse and it is getting abused a lot.  But it still works.  It helps a lot of people make a lot of money. And until it is so, it won’t go or even change much.
Now the question is - what are the alternatives?