I am surprised that the comments haven't mentioned the role of SEO in Wikipedia's growth and defensibility. Wikipedia's habit of deep interlinking helped it rank back in the early aughts when the SEO rules were rather simple. Add to that the subdomain-driven localization strategy and many other moves that were considered SEO best practices back in those years when the on-page factors used to matter. But that was just…
That's one version. Another version, that I know will go over very well here, is that some have invested a lot of money to bring high quality, accessibly-written off-line content by experts in the field to the Web, only for Wikipedia editors to poorly rewrite it in thousands of articles and rank over the original content in Google. And then Wikipedia started using non-follow links so the original sites got no benefit…
The way Wikipedia should work is by sourcing verifiable facts from reputable sources, and copyright violations are not allowed. I don't understand to what are you referring with "high quality, accessibly-written off-line content"? Britannica isn't high-quality and journalism isn't written by experts in the field.