These two giants have monopolized a large portion of the retail market. The only reason amazon pays their workers more is because they don't have to maintain a storefront, it's much more automated. However recently even some of the Amazon employees are being replaced by machines (drone delivery/robotics).
We denied the growth of so many small businesses because there was no cap for these giant corporations. Using their profits, they can invest in bulk deals to get the product cheaper then their competitors. Amazon has a huge advantage, they also own Twitch which has become a massive market. And some people in North America have became so lazy going to the store is the ultimate struggle so they'd rather order everything.
RE: Walmart Vs Amazon: Who Will Top The US Grocery Market?