Because you have the belief that you can generate a better ROI internally invested. Returning cash to shareholders is usually a negative sign for the company as

Because you have the belief that you can generate a better ROI internally invested. Returning cash to shareholders is usually a negative sign for the company as it means they don't think they believe other companies will be better with the investment than themselves. It's only recently in the share-buyback age that this investment is rarer. The classic example is Amazon which was technically profitable for a while, but did not return shareholder cash for many many years, choosing to invest instead.