> Coming from the same factory line with the same quality control, just rebranded (Costco famously does this a lot)

Costco famously shops around aggressively for quality products -- not premium, but not crap -- and usually from big manufacturers who are already making excess supply.

Is common for supermarkets, too. Kraft can only get sub-par cheese one quarter so they make the same product but sell it as a white label option for lower margin. The factory line keeps running, product gets moved, inventory gets cleared, and margin is slightly lower but acceptable.