In a mature market, marketing/advertising is zero-sum because it shifts demand from one supplier to another without altering the overall demand or supply.
The obvious case is a commodity, like wheat or soybeans or oil, where nobody bothers branding it at all until they get to a retail product. In the retail marketplace, the primary differentiation between one kind of cleaning product and another is the marketing, advertising, and associated superficial differentiations: coloring, fragrance, and so forth. That's why the largest advertising budgets are for companies with similar competitive products: GM/Honda/Ford/Nissan/Toyota/Hyundai; Procter&Gamble, L'Oreal, Estee Lauder; Samsung/Sony/HP; Progressive/Allstate/State Farm.
They aren't advertising to get new customers into the market: they're advertising to shift customers to competing suppliers.
Samples pulled from adbrands.net list of top 100 US advertisers. There are many, many more clusters there to illustrate the point.