Because ultimately shareholders (barring kooky Google stock arrangements) own the company. Practically, they select board members (Apple recently added the "3%+ stakeholders may nominate new members" clause), who select the CEO, who would propose and implement such a scheme.

So distributing it to employees, while noble and just (imo) would require shareholders to vote against their own immediate interests.

In practice, there's probably some friction, but you can damn well believe with numbers this large Tim Cook would be sued in a heartbeat if he attempted to implement such a scheme.