You mean why have they 'grown' ? Because people aren't inundated by TV ads anymore to think that Tide is better than Kirkland. It's not by the way.
I've never been worried about buying yellow-label products when I go grocery shopping. The lesbianic wheat squares breakfast cereal and so on. In most cases there's not much difference. Especially when it comes to products that just don't require a whole lot of thought. I often buy canned mushrooms... I don't think anybody can tell the difference between "no name" and "Money's" canned mushrooms. You can't screw up the recipe for mushrooms. Lots of other goods are similar. Rice, pasta, butter...
One product where I've tried "no name" versions and gone back to the brand name is Campbell's soup. I use mushroom soup in cooking, and find that "no name" versions are just too salty and don't taste as good. Campbell's is one of the brands mentioned in your article, but IMO they're one of the examples where it's worth paying the extra.
On the other hand, I really like many of the President's Choice products. I've been buying the PC "Blue Menu" frozen lunches lately, and they're very good. I prefer PC coffee and even "no name" coffee to Maxwell House and Folger's, and only buy the latter if they're on mega-discount. And Hills Brothers coffee... if a truck carrying a load of Hills Bros coffee crashed and there were cans of Hills Bros coffee all over the road, I wouldn't even cross the street to pick one up. Yuck.
I stayed in a town in Michigan that only had a Wal Mart. I have never been in a Wal Mart.
I generally steer clear myself... there are occasions when I need a number of things and I'm in the area and it's just more convenient to get everything in one stop. We could start a "Walmart Culture" thread for trashy videos about trashy things going on in Walmart.
-k