If no one is seeing them, how do we know they exist?

In the above example, someone is paying for them. "In 2021, the agreements between brand owners and films and television programs were worth more than US$20 billion".

Paying for them does not causally mean that you can not see them. I well believe marketing people think they're extra clever.

I'm pretty sure you are very unfamiliar with how ads actually work.

The best advertising is word of mouth advertising and smart marketers seek out people of influence in their communities to spread their products. This was well known in marketing long before the term online influencer was a thing. It's very hard for most people to even notice this kind of advertisement is even happening.

My first reaction when a friend tells me about a product is, that he/she must've seen it on social media.

- Do they actually own the product? - How long have they owned the product? - Show me how it works. - How much have you paid? Else it's worthless to me, but I'm happy for him/her

Clarification: Some people can see some of them, some of the time.

Eg. Some brand used in a movie.

Usually brands pay for that screen time, but it’s not very obvious that it’s payed advertising.

Huh? I don't think there is a person on earth that does not know the BMW James Bond drives, is not sponsored. Is this really the expectation? I don't believe it.