But to make any sort of impact on wiki you need to be able to generate content. So anyone can play, but only good players have any desire to keep playing. It's an intelligence test of sorts to be able to edit a wiki page. It's not rocket science, but it doesn't appeal to the TV watchers. If it doesn't appeal, they don't participate, which leaves those of us who read and write to get on with rational discourse.
Folk have time to think, often days or weeks, before they follow up some wiki page.
So what people write is well-considered. See WhyWikiWorks and WhyWikiWorks for more.