> Maybe there's no cost to a page sitting on Wikipedia describing, like, some guy's special attack from Naruto.

There is a cost, but it's measured in hours of maintenance labor not bytes of storage.

If Wikipedia wants to maintain a semblance of accuracy [1] in the face of declining participation, it needs to concentrate its labor resources rather than spread them out.

[1] which IMHO is vital given its unwise prestige as arbiter or truth