Whenever I read these articles I always forget that most people don’t buy in bulk. I do most of my shopping exclusively at wholesale clubs and only use grocery stores for the things like spices or other ingredients we may not need a ton of.
Order dry goods by the 25 lb bag from nuts dot com or other suppliers. The effective price I pay is sooo much lower than what the average person spends. There’s some initial investment for pantry shelving, jars / bins for storage etc but it pays off very quickly.
I don't really buy in bulk, but for two adults total, I spend $70-$120/week at a major grocery store. Basically, clip their online coupons and shop the sales. So I'll pick up some goods in bulk, if it's something we use enough of and it is on sale that week. We also don't buy meat because my wife is a pescatarian, so most meals are vegetarian or fish.
It's not too difficult to keep costs down, but I can see if someone has a picky household, can't buy anything in bulk when it's on sale, or is bad at planning (ie, lots of impulse, junk, and prepared food purchases) how it can add up quickly.