If you wrote a blog about leatherworking and wanted some
ad money, you could go to a leatherworking tool company
and say "I have this much traffic and its 100% people
interested in your product becaus
It does not work.
For this approach to work, you need somebody who...
1. Is good with the actual subject matter (leatherworking or whatever)
2. Is a strong writer/communicator
3. Has the "salesperson" personality to go and promote their blog to potential companies
4. Has the TIME to promote their blog to potential companies, deliver metrics so they know what kind of exposure they're buying, etc
5. Has the appropriate technical chops to run/publish a blog, handle ads, set up analytics, etc.
Those are disparate skillsets. You are going to exclude an AWFUL lot of good leatherworkers who'd otherwise be good at this. Sure, the occasional unicorns who combine these skillsets exist.
Just like there are a certain number of people in the world who are competitive skateboarders and... are also taekwondo masters or world-class violinists or something.
And if you're lucky maybe 0.1% of that remaining 0.1% will actually have the time to pursue something like the venture you describe, which tends to rule out folks who are already working 40+ hour weeks and have kids and such.
In reality, we're talking about an operation involving several full-time people with a breadth of skillsets to make this kind of operation a sustainable business.
A lot of podcasts and streamers do kinda make this work, but are generally part of networks and in the end are still beholden to advertisers whose businesses are an odd fit with the subject matter at hand anyway -- like all the tech and true-crime podcasts who sell ads to Stamps.com. It's not really the smoothly-integrated seamless bespoke ad paradise you want.
Also now they've effectively censored you about the dangers of paying to have a spy camera in your house that collects all footage and sends it to law enforcement (and anyone else with access).
If you wrote a blog about leatherworking and wanted some ad money, you could go to a leatherworking tool company and say "I have this much traffic and its 100% people interested in your product because why else would they be on my website reading about this niche leatherworking technique that only you and I and my audience care about, lets make a deal." I bet that pitch would land a handshake.
With streamers/influencers being an entire industry these days, there are probably a lot of boutique agencies who do all this legwork of connecting company with highly specific products to your interested niche audience for you. And if the model changed where this would be how advertising is now done, you would see a lot more of these advertising agents at every economic spectra making these deals on behalf of any sized company or website.