Sites are lazy and greedy. They throw dozens and dozens of 3rd party javascripts into their headers, that punish and annoy people for not using an ad blocker - they slow the site down, bloat the memory, consume energy, track the user and festoon the page with garbage. As soon as people hear that an ad blocker is a thing, then of course they leap at the chance of using one.
It would be straightforward for sites to insert ads into their content - make the ad urls, images and links indistinguishable from actual content. i.e. serve them up from the same domain, from non predictable paths and use html structure where ads and content are intermingled. Even if an adblocker wanted to block the ads, there are no patterns that work and every single site would require different rules. But that requires effort. I suppose we should be glad that sites don't do it.