Amazon's free cash flow rises year over year (apart from the post-COVID period) [0] while Walmart's doesn't [1] and price multiples are largely determined by expected FCF over time not directly revenue/EBITDA. FCF rain or shine maps roughly onto possibility of paying out dividends/buybacks, which determines the value of an equity in capital markets ("discounted present value of a company's future cash flows").

[0] https://www.macrotrends.net/stocks/charts/AMZN/amazon/free-c... [1] https://www.macrotrends.net/stocks/charts/WMT/walmart/free-c...