That's the thing, though. If these ads show you deals for things that you would actually be buying anyways, then those ads are doing a terrible job.

They don't ever want to be truly relevant to you, because they don't work for you. They work for the advertising company. And against you.

Sure, they can't sell diapers to someone without a baby. But if you did have a baby, you can be sure that they won't be advertising the cheap and perfectly good diapers that you would be getting anyways or that you really should know about.
They'll try to have you spend money on expensive brand diapers that are really not worth their money. Can't be, because obviously some of that price pays for advertising.

Also, they will try to convince you that they are worth their money, because psychological warfare is the norm for advertising these days.
The idea that they serve to inform customers and create the necessary transparency to allow capitalism to self-regulate, that's at least since the internet became a thing, just complete nonsense.

Because we now have a lot of transparency. If I want to buy diapers, I can hit up the search engine of my choice and be offered a decent diaper selection.
An ad trying to grab attention is really doing a disservice to transparency, because you're then less likely to utilise a search engine.