Seems like it would be a good idea for Google to implement a basic quiz that goes over the TOS and covers specific things like clicking on your own ads and such.. and is such that you can't actually use your account until you pass. I would normally think such things are unnecessary, but I think in this case it might help.
Why do they care? People click their ads, they find out and refund the money. I'm sure it is very simple to match IP address to clickers and logging into an account...especially when most people click, then log in to see the amount...
Why do they care? Because a certain percentage of people who do this are simply ingorant... And an ounce of prevention is worth a pound of cure. They struggle in some cases because the try to automate things. Making the TOS clear and upfront in a manner that people must understand and accept and move forward can only make things better. Not sure what kind of businesses you are used to running, but telling me that the alternative is spending ongoing human resources to investigate and refund as opposed to a one-off project of creating a quiz.. Well it is a no-brainer which one makes sense... They care because it makes sense and would likely save them money in the long-run.