Why is Walmart so popular in the US? What kind of services do they offer that others do not or do they only?

have cheaper/lower prices?

I think for most people it is that they have cheaper/lower prices and pretty much everything in one store. A lot of people are lazy or, to be fair, short on time and don't want to go hunting for best prices at various stores when they can find it at one location. I personally avoid Walmart as much as possible but that is just me.

Edit: To be fair again I should note that most grocery stores do tend to overprice and not all cities or towns will have a grocery store that has affordable prices. I lived in a place where there weren't any stores but the big Smiths type stores now I have Aldis which has really good prices on groceries.

Cheaper lower prices..some grocery items to getting your car repaired, clothes, linen, pharmacy. Some super walmarts have optical, photography studio, hair and nail salon, fast food , full grocery stores and everything else...their prices are usually always the cheapest or pretty darn close. Their generic brand isn't that bad either.

I like to go to the walmart supercenter were they have groceries because I hate having to go to different stores to get what I need. Plus the price of paper towels, toilet paper, etc are much more pricey at an actual grocery store.

I am Brazilian and here in Brazil the Wallmart is not also a very popular market, the foreign market that more it pleases for us is the Carrefour.

Cheaper groceries than the other grocery stores around.
Other stores - greedy - with incredible markups.
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cheap prices and special offers.