The money came from people selling (or trying to sell) products that other people want to buy for the price that includes the ads, as it's valuable. This is far better than the old school ad industry, which made advertising much more expensive and products more expensive.
$400 billion was spent on advertising alone in the US in 2023. In 1970, that number was $19 billion ($150 billion in 2023 dollars). Relative to GDP, that’s and 0.014% and 0.018% respectively. Depending on how you want to argue, there is either more spending on advertising (in dollars) than there was 50 years ago, or about the same (in relative GDP). Neither would account for products in the past being substantially more expensive than they are today.
That is ignoring the many moral arguments against targeted advertising, unnecessary consumerism, etc.
