OF COURSE the law of supply and demand works. Its how free markets self-regulate. The point is that there are no free markets!

Both supply and demand can be interfered with by producers using mechanisms like advertising, political lobbying, cartels, monopolies, "trade associations", the list goes on. They can flood markets, dump commodities, restrict production, a variety of predatory tactics that allow them to wage war on their competitors, not to mention the endless war they wage on their customers, employees, suppliers and stockholders. And capitalists have the money, power and tools to do this. They collect information and guard it jealously. They ally themselves with their "competitors" to agitate in their mutual interest, if not by all-out brazen self-serving collusion and price-fixing. They viciously oppose any attempt by their victims to organize, unionize, or investigate their activities. They use their money and influence to buy politicians and sway elections. Why do you think organizations like the NRA and OPEC exist? Their sole purpose is to manipulate the "free market". Why do you think university business schools have "marketing departments"? To teach their students how to frustrate the automatic mechanism of supply and demand.

Economics is a human activity, it is governed by human decisions and naked self-interest. The thought that it somehow depends solely on immutable and impersonal natural laws, like physics, is a convenient fiction deliberately foisted on us so we will docilely accept what real businessmen actually do. I'm sorry, but there is no magic law of economics, no invisible hand that will punish evil businessmen and help out honest consumers. There is no mystical force that will ensure economic justice, and if you believe there is then the capitalists have done their job well at indoctrinating you and conning you into accepting things the way they are.
They may even have convinced you that if you believe them and work with them they will cut you in on a piece of the action. That's why we have governments and regulations and that's why capitalists fight tooth and nail to stop them. "Without proper government, the strong will always take from the weak."

The purpose of a business executive, particularly a marketing executive, is not to ensure that supply and demand, production and consumption, are optimized and matched for maximum efficiency. It is to ensure that sales and prices are manipulated in such a way that PROFITS are maximized. Sure, sometimes supply and demand overrides these stratagems and the consumer finds a good deal, but it is by no means guaranteed.

When we say X is a good businessman, what we really mean is he is good at gaming the law of supply and demand.