Investors could start getting angry if they feel that Google is blowing large amounts of cash on endeavors that continue to fail. By doing it this way they get a major stake in the potential success of their spin-offs, but they are able to continue delivering profits rather than sinking cash in one black-hole big idea after another. It's probably a matter of walking the line between short-term value of the already successful business versus long-term but riskier value of the potential moonshots.