> How is this any easier or more effective than just having a website that hosts its own advertising assets

advertisers REALLY don't want you to do that because it's far too easy to cheat.

I expect that they are already cheating as much as possible to convince their customers to continue paying for advertising that has a negligible effect on the bottom line.

Adtech and PR firms would have you believe that it is impossible to sell a product or service online without first paying them $10k/m. It's also why google search is so awful - if they could get you the information you were looking for they are sidelining their customers, so their search has to, by design, be limited so that their customers are more prominent in the search results than non-customers.

Note: I'm not saying that this is by design; they could get to this stable equilibrium simply by each isolated team within search, advertising, etc aggressively pursuing its own metrics.

Right not it is not hard to write an adblocker, just block network requests and DOM elements (regardless of whom hosts of proxies them).

A browser in a browser would make blocking dom as hard as attaching a debugger and manipulating a price that has been hardened.

Network requests may still be able to be blocked, but it is going to make ad blocking harder.

Hell, the inner IFrame is probably going to get around IFrame recursion and domain rules too.

We're going to eventually end up with IFrame fork bombs, and IFrame topologies that cannot be meaningfully mapped to Euclidean space (amongst all the other privacy, user control, etc. concerns, of course).