I'd could argue that the "excess" cash might be better used to raise employee wages, reduce work hours, etc. etc. All those things that make human workers a bit happier but c'est la vie
Exactly stock buyback are a 'too easy' way of driving up stock prices. You want companies to use their capital to increase the real value of the company. At the same time you want to discourage CEO's and stockholders from looting the corporate till.