Which is why you lower the corporate tax rate. This gives companies more leverage to use the investment money they get. They can purchase assets, fund R&D, buy smaller promising companies, and hire more labor.
Right now they will use any savings to buy back stock - that's the rational thing to do and makes the investors happy. But if we tax investment income progressively then buying back stock is great for the US Treasury - someone has to sell that stock to the company buying it back and it's taxed more!
It becomes more reasonable to reinvest that money from a corporate perspective. This is what the investors will want done.