A trip to a hypermarket is a comparatively big deal - you typically have to travel further and you are also going to spend more money. So to the extent budgets are tight, people will make do with more frequent local trips, accepting the price hit that follows.
The other issue (at least in the US) is Amazon and other online retailers. Suddenly people can get a decent price without having to make the trek to a hypermarket.
The final point is competition from the membership-only stores - they carry a much smaller inventory and hence can be more aggressive on pricing.
Those are all excellent points, but there’s an even more compelling reason that the hypermarkets were hugely popular in such countries as Brazil during the 1980s and 1990s: the high inflation rate!
When annual inflation is running in the triple digits or high double digits, you want to buy everything you need as soon as you receive your paycheck. Waiting even one day (or a portion of a day in extreme cases) can result in paying higher prices. Under these circumstances, shoppers want to make as few stops as possible to get what they need, and this plays into the strength of the hypermarkets.