The services they provide have been of incomparable quality to any other offering in the US. They made free 2-day shipping and free returns the baseline. Amazon lockers provide online shopping opportunities to those not privileged to own a house with a secure front yard (I do wish shipping to amazon lockers was possible from other online-only retailers). And in truth the vast majority of amazon’s income is still invested back into the salaries of its workers and building infrastructure — they have notoriously thin profit margins outside of AWS. Bezos’ fabulous wealth comes from stock.
Edit: I’m not affiliated with amazon and my acquaintances had very stressful experiences working there. But as a customer I really appreciate their service