Why are search clicks worth so less?

I have never quite understood this. I would have thought it would depend on what people were searching for, but it always seems to me there to be too many 2-3 cent clicks.

 

I was thinking the same question.

 

Maybe its just been coinsidence that the keywords have all been low paying ones. I always thought they were worth the same as normal ad units.

 

There is logic in that, but reality seems different.