Prices more expensive because of it's customer base - ability to pay and expectations of quality. Because it's expensive, it's not as crowded as Lulu, FFP, etc. so some people prefer to shop there for the convenience.

I shop in carrefour, Lulu and FFP cos I'm on a budget but go to Megamart if I'm in a hurry or only have 1-2 items to get as it's on the way home. If buying in bulk, that'll bust my budget.

FFP is also on the way home but if only 1-2 items, I avoid the crowds esp. since some strangers (guys) tend to use any excuse to come too close for comfort.
/Buying in bulk, I use a shopping cart ;)