The did it for the same reason every megacorp does anything: money. Their stock price jumped over 5% when they showed this fake demo. It has since come back down a bit, but it is still up about 3.5%.

"Don't be evil" was really a warning of intent.

   The Devil went down to Google
   He was lookin' for a soul to steal
   Google was in a bind 'cause they were way behind 
   And willin' to make a deal