Historically, marketing cost was a small fraction of manufacturing cost. Gradually, marketing cost took over in many sectors. STP Oil Treatment was noted in the 1960s for being mostly marketing cost.[1] Marketing cost began to dominate in long-distance telephony, in the era when you could pick your long distance company. Retail Internet access is dominated by marketing cost.

The total amount of consumer products that can be sold is bounded by consumer income. Advertising mostly moves demand around; it doesn't create more demand, at least not in the US where most consumers are spent out.

Think of taxing advertising as multilateral disarmament. Advertising is an overhead cost imposed on consumers. If everybody spends less on advertising, products get cheaper. Tax policy should thus disfavor zero-sum activity.

[1] https://en.wikipedia.org/wiki/STP_(motor_oil_company)