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

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".

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.

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.