Because it's a kind of fraud. If you cheat someone out of $1M by tricking them with a Nigerian Prince scam, you go to jail. If you cheat someone else out of $1M of profits by selling their trade secrets to a competitor, you should see a similar punishment, right?
Intellectual property isn't physical property. Google lost absolutely nothing in the exchange except the possibility of perpetual monopoly on this particular algorithm. Google still owns it, and they can still profit from it, the only difference is that they now have to actually compete.
Stealing IP via piracy will put you in jail too, though. I'm not trying to make a case for whether or not trade secrets (or movie downloads or software) "should" be protectable via law. I'm stating bluntly that it is.
