That's an interesting question. To oversimplify it, the value of a stock of essentially a wild-ass guess about how much cash one might be able to pull out of a company eventually per share times the number of shares.

If I a company isn't paying dividends or buying back stock, and we (the shareholders) can't coerce said company into doing so at some point, it's essentially an indestructible piggy bank in which money evaporates while you helplessly watch.