The paradox is that many academics see these gaps and flaws in the coverage of their own favourite subjects, yet do nothing to correct them. Let me discuss three possible reasons for this passivity: fear of Wikipedia, lack of time, and laziness.
The jungle outside the ivory tower
Attracting and retaining academic contributors has long been recognized as a challenge by Wikipedians, to the extent that there are guidelines on how to do it.
Academics may fear to collaborate with generalists on an equal footing, and to have their work changed or deleted by others. This fear is largely unfounded: Wikipedia has mature mechanisms for moderation and conflict resolution. And in most subjects, contributors are too few, rather than too many. Moreover, generalists can do plenty of useful work on style, structure, clarity, sourcing, etc. (They would even be able to help with writing research articles themselves, if given the opportunity.)
Academics may also not be eager to comply with Wikipedia’s own guidelines. In particular, Wikipedia strives to be much less technical than the academic literature. For example, the article on the AdS/CFT correspondence is a “featured article”, i.e. an article of top quality according to Wikipedians, and it contains only one equation. However, the guidelines are not enforced strictly, and Wikipedia’s “fifth pillar” is that there are no firm rules. In subjects that are underdeveloped today, Wikipedia will become what contributors will make of it.
If Wikipedia’s functioning sounds suboptimal to them, academics should consider the deeply flawed system of scientific communication that they experience in their work, and compare the academic literature with Wikipedia in terms of quality and reliability.
No time for altruism
The main activities that advance academic’s careers are doing research, writing articles, and looking for money. Writing in Wikipedia is not among them, and could be dismissed as a waste of time.
This would overlook the fact that academics already practise career-neutral activities, such as popularisation and peer reviewing. It is to these activities that writing in Wikipedia should be compared. Wikipedia probably reaches more people than any other medium of science popularisation. And contributing to Wikipedia probably advances science more than writing reports for a handful of readers. Vast amounts of time are spent reviewing unworthy articles, out of a misplaced sense of responsibility towards a system that mostly fails at filtering and improving the literature. It would be more constructive to spend some of this time on Wikipedia.
Is laziness a good excuse?
Writing good and complete Wikipedia articles of course requires much effort. I considered myself ready to start an article on two-dimensional conformal field theory only after writing a review article and giving lectures on the subject, plus updating the article on the Virasoro algebra. However, many useful contributions can be done with little effort: correcting a mistake, making a sentence more precise, adding a reference, or updating an obsolete fact.
Moreover, the collaborative nature of Wikipedia allows each contributor to do what is easier to him. This means not only writing on the subjects he knows best, but also focusing on the aspects of the work that he prefers: clarifying explanations, structuring articles or groups of connected articles, making figures, or choosing references. Everyone can, and should, contribute according to his tastes and abilities.
I have argued that neither fear of Wikipedia, nor lack of time, nor laziness are good reasons for academics not to contribute. The relative scarcity of academic contributors might be better explained by pure and simple inertia. The problem might solve itself when today’s academics are replaced by digital natives, but it would be a pity to wait until then.
Wikipedia is not only a powerful tool of scientific communication, but also a world wonder whose existence shows that humanity is capable of collective wisdom. Contributing to Wikipedia should be part of the mission of academics.