They agreed with you, that if BB has the exact same item as Amazon, they would match the price. It would work for "unique" products that aren't just very generic, easily replaceable, and don't have a significant variation, where a customer would prefer a very specific model of the item (like headphones, videogames, movies, tvs, monitors, etc.). If you want to buy Die Hard trilogy on Blu Ray, you probably won't be satisfied with buying Rambo trilogy on Blu Ray, despite them being somewhat similar. You care about the exact model of the item here.

But if you just want to buy something generic, like a USB-C to USB-C cable, it isn't something that people have brand loyalty towards, it is something very generic and easily replaceable. You don't care about the brand, you just want a USB-C cable that supports Thunderbolt 3 spec and is at least 6ft long. On Amazon, you will have bajillion choices from different brands across all price ranges. At BB, you will have a couple of brands that are probably not even on Amazon for various reasons (e.g., it could be a BB exclusive version of that item) and are significantly overpriced. And you cannot just price match any USB-C cable to any USB-C cable that meets the same spec and is the same length, it has to be that exact same model.

So, for example, if the "premium" brand version on Amazon costs $20, cheap one costs $8, and the only version from a completely different brand available at Best Buy is barely even the same quality as the "cheap" one from Amazon but costs $40, it makes no sense to buy it from BB.