Various firms do, both large and small, but it is extremely difficult to compete across so many fronts without a massive amount of capital (logistics, distribution, negotiations with manufacturers, real estate, marketing, product development, etc).

The return on investment for such a massive deployment of capital isn't huge and Walmart could adopt your strategies at any time, undercutting your value proposition. I'm also 100% certain there is a lot more collusion going on but with CEOs smart enough not to write it down in an email.

That said, a tightening labor market is forcing Walmart and other competitors to slowly raise pay.