Setting aside the fact (pointed out by several siblings) that they do buy back stock...
Why should they? Who does it benefit? Not their customers. Not their products. Not their future prospects. Not their employees, for the most part.
...Oh, the shareholders? You mean they should throw massive amounts of money—their hedge against future problems—into enriching people who are, for the most part, already vastly wealthy?
I'm not super enthusiastic about stock buybacks, but to my knowledge, pretty much 100% of Apple employees are eligible for the discounted Employee Stock Purchase Program (which is a no-lose proposition, if you can afford to defer part of your salary for 6 months), and at least in some years, all Apple employees got some outright stock grants, so the interests of "employees" and "shareholders" may be more aligned than you make them out to me.
What else should they do with it? Just hold it so that they can hedge against future problems? How much do they need for a hedge? 1 year of expenses? 2 years? 5 years?
What should they do once they reach your hedge number? Just keep hoarding?
What do you do with your salary? Do you just put it in your bank account or do you invest it? If I’m Apple, do I really want to become a company with an investment arm? If I’m an Apple shareholder, do I really want Apple buying a broad market index fund and then paying corporate taxes on that and then spitting off dividends to me rather than just giving me the opportunity to invest in a broad market fund myself?
Why should they? Who does it benefit? Not their customers. Not their products. Not their future prospects. Not their employees, for the most part.
...Oh, the shareholders? You mean they should throw massive amounts of money—their hedge against future problems—into enriching people who are, for the most part, already vastly wealthy?