The reason blocking is so easy and works so well is because everyone got lazy.
Publishers want ads but don't want to actually do the job of selling them; ads used to be free money, and this is coming to an end.
Ads from their own domain would be a little harder to block, especially because blocking would have to be done on a page-by-page basis (or at least, website-by-website).
Personally, I do not block first-party ads (i.e. ad images served from the same domain as the original content). For me, the point of using an adblocker is to reduce attack surface and tracking opportunities.
I see, of course, that I'm likely not representing the majority of adblock users.
I have ublock myself for privacy concerns, but I install ad blockers on all my relatives computers just because they are trustful and dumb enough to click any shiny green button that says "Download". Otherwise, I have to pull my hair when I look at their computers full of crap, which they can't explain how it got there. If the internet with ads wasn't such a dangerous place, I wouldn't do it in the first place.
Publishers want ads but don't want to actually do the job of selling them; ads used to be free money, and this is coming to an end.
Ads from their own domain would be a little harder to block, especially because blocking would have to be done on a page-by-page basis (or at least, website-by-website).