greed is the no. 1 reason but they all don't know that by keeping patience they can earn more and for a long term
Malfunction in Algorithm: Google uses some algorithms (e.g. genetic algorithm/programming, neural network, clustering) to fight click-fraud. Basically, it detects patterns in the clicks and check them against fraud patterns. The thing is it occasionally fails like any anti-spam filter, which also makes use of similar algorithms. Therefore, some legit publishers get booted just like some legit emails that are routed to spam folder. Although Gooogle depends on its employees to make the decision to ban or not, the malfunction of the algorithm already set 80% of a publisher's faith. Sabotage Attempt: There're competitors who do business against each other fairly, but there're also those naughty enough to sabotage their rivals illegally. In adsense context, someone who hates you might go your website and click bomb the hell out of the ads. What's worse, he calls his employees and friends to generate hundreds of invalid clicks. This will surely lead to your suspension of your account several days later. Over-optimization: Blending the ads perfectly that users think the links lead to some pages on your website. Best example is blending ads in a row in the middle of a table, like in second row in vbulletin forum list, thread list. Another good example of over-optimization is putting ads near icons and under dynamic javascript menu.
Over Optimization..... This is kinda unfair, they really can't draw the line to what is over or just well optmized, its a fine line...since google ill even give you the tools to best blend the ads..
Do you mean that I can be banned for getting 4$ or more per click? Actually, Google is the one who decides on how much you make per click...
10) abusing the rules 9) violating the rules 8) circumventing the rules 7) not following the rules 6) being in violation of the rules 5) encouraging others to break the rules 4) not being in compliance with the rules 3) disregarding the rules 2) breach of the rules and number one: BREAKING THE RULES