The price of Amazon stock is ultimately supported by expectations of future dividends. The same is true for other stocks too, of course.

Whether or not the company has paid out dividends in the past is a good predictor of whether they'll do so in the future, but it's not the only such predictor. Having accumulated a mountain of cash but using it to invest in the business (buildings, equipment, and other productive assets) is another. Probably better, at least in some sense/cases.

The other way in which the stock is supported is by other people's expectations of other people's expectations of future dividends, and so on. I.e., speculation. Still tied to dividends, just in an unhealthy and volatile way.