How does bi-wiring work?

"Bi-wiring" is not a marketing ploy.  But may not be the best way to get the most bang for the buck for some listeners.  All things being equal, if you break out the total gauge of one cable into 2 cables, you'll be adding manufacturing costs in producing 2 cables, complete with another outer jacket, terminations, and additional labor. 

Part of the cost/performance bi-wire "argument" is that the higher frequencies do not require as much gauge as the lower end.  Therefore, put less of the "good stuff" (i.e. better material) on the top end thus extracting the best sonics from those materials, and bulk up (add meat) to the bottom end with less expensive materials to get more gauge.  This optimizes the cable budget using the most cost effective materials where they'll yield the best sonic benefit(s).

Some are not fans of additional jumpers and connections with a single cable/biwire connections, and prefer the straight line from the amplifier to the speaker input terminals that bi-wiring provides.

We can argue this until we figure out how to plug a digital bitstream directly into our brains.  I think it's a cost/performance conversation with no "winners" or "losers" in sonic performance if it's done "right."

We need to recognize that the concept of bi-wiring came from speaker manufacturers, not cable manufacturers.  Some of the most brilliant, and respected minds used real science to reach their conclusions.  Based on my limited understanding, when a woofer is moving it creates back EMF, thus interfering with the upper frequencies.  I would suspect this phenomenon can be measured, and validated.  The concept of bi-wiring caught fire with the majority of "legit" speaker companies adopting it, and touting its sonic benefits.  This may be the case of "mass duplification" (lots of people being duped) or some of the best of the best talent in the industry saw and heard something real here.

It is not the function of cable companies to debunk manufacturer's marketing materials and methods.  If so, they'd rip them a new one for the crappy cables they use internally and their sonically degrading "high manufacturing/service efficiency" connection/termination methods.  So, offering up a product that embraces a (respected) manufacturer's credibility position is neither blind, nor unethical.  Just good business, based on a solid foundation.