WebProNews

...If decreasing the clickable area of an Adsense ad is the direct cause, why would a smart company like Google do such a thing? ...

To ask such a question is to show an ignorance of corporate responsibility, and healthy business model (long term) so let me help explain it to you.

By reducing the number of accidential clicks you get advertisers that get what they pay for. Anything else is is irresponsible and some might go so far as to say that knowingly allowing it to continue (with solutions available) is also unethical. 

Since advertisers  ultimately decide to halt or continue advertising campaigns based on ROI -- accidental clicks only serve to reduce the" R". Ultimately, advertisers will leave for other sources, reducing competition, reducing CPC, and reducing revenue even further for google.

Ultimately the "why did google do it" questions can only be answered one way...It's responsible and long term that is good for google.