They do require a certain degree of technical understanding, but the extension system on most browsers is fairly mainstream so I don't think it's for this reason alone.
Can it be as simple as the idea that almost all of media is universally disincentivized from talking about them? Of course there is a lot of content on ad-blockers out there, but the pressure may still be high enough to suppress cut-through to the mainstream. If that's the case it would be a nice example as to the extent of media influence more broadly.
This article is a case in point, where you would have thought that ad-blockers may have been relevant. And as a side point, perhaps also a good example of where you don't even have to be rich if you are knowledgable. Technical literacy is in itself a kind of digital affluence.