The goal of advertising is to hammer you with the same content again and again until your brain associates something with the product. Like shampoo associated with what you see everyday in the advertisement.

However in order to do this, whether you are selling or buying, you have to have the scale. And the scale of big players is now too big to compete.

And even if you do, your infrastructure will run on any of these big companies who can do anything to your traffic to keep their business and later pay fines for unethical practices that are minor compared to the profits.