What is Wikipedia failing at currently that decentralizing it would make better?
Just like reddit (and many other services), its a centralized US-based service, has a history of scandals and conflicts of interest, has ties to the US state department, and is dominated by a small group of editors (despite its perception as being a universal unbiased knowledge store).
There’s definitely a need to decentralize knowledge, move it away from US control, and allow the collaboration that activitypub provides.