There's also an asymmetry of information and of control. In a downturn, Bezos has full visibility into where all of Amazon's COGS is going, and a number of levers he can turn to axe some of that spending, reduce future investment, or shed unprofitable business lines. Wall Street has virtually zero of that information (they get the consolidated financial statements, but none of the detailed breakdown) and zero of that leverage. Therefore, it's significantly less risky to Bezos to run on razor-thin margins than it is to an Amazon shareholder.
Same reason that founding a startup is significantly less risky for a world expert in its problem domain than for a random investor in that startup. The founder has full knowledge of the domain and a lot of levers they can pull to adjust strategy; the investor has none of that. That's also why many VCs require terms to reduce their risk (liquidation preferences, participation, anti-dilution, warrants) or increase their control (board seats, voting rights, information rights).