If we take the Walmart example, you can see the endgame of their business model play out. You have a store which grows into a small chain, then into a regional chain then into a national and multinational chain. Their success coming from organisational efficiencies, keeping costs low and benefiting from economies of scale.
However, that trick only works at certain scales. Once you reach the scale Walmart is at, then your ability to keep costs low starts to impoverish large chunks of society (workers and food producers). This triggers a reaction, strikes, boycotts etc. All of which are ultimately very bad for business and the economy and points to their model being unsustainable.

There was a time where monopolies got dismantled by governments (Standard Oil being a notable example). However, the appetite by governments for doing this seems to have waned.