For an outsider it may be surprising the know, that Wikipedia and OpenAccess have not much in common. The first impression is, that a typical Wikipedia article has footnotes and is discussion science, while the ordinary paper from Elsevier is doing the same. But, if we are investigating the history of Wikipedia and normal academics there is a huge contrast. The main difference is, that Wikipedia is working according to the hacker mentality. It is some kind of GNU project in which everybody is welcome, as long as his contribution is right; while academia works slightly different. Academia works with with academic societies. That are student groups which have something a journal and it is very important to differentiate between a member of the society and the rest of the world. For example, the IEEE society works with that principle, but there are many other of these groups. The main aspect of academic societies is, that not the knowledge is in the middle but a person.
Let us investigate a short example. An ordinary people wants to be a member of IEEE. How can he do so? Answer, it is not possible or only over a long period of time. The normal way of become a member is biographical driven. That means, the must learn 18 years in a normal school. Get a degree. Then he is attending the university, get also a degree. Than he is attending the PhD program (which costs a lot of money), and after this procedure is over (which takes around 30 years or more) he can become a member of IEEE society. That implies he has the right to read the journal and write articles by his own.
In contrast, to become a member of Wikipedia is much easier. He can sign up for an account, and 5 minutes later he can vandalize the first article. He must invest not 30 years, and no money. That is the main difference between Wikipedia and serous academia.
Between both poles there is an interesting in-between-service available, called Academia.edu. Academia.edu works with with Wikipedia principle. That means, the general idea is, that everybody is welcome and after 5 minutes he can upload his first paper. That is perhaps the main reason, why Academia.edu is outside of real science, because this workflow contradicts the model of learned societies. Academia.edu, Wikipedia and Unix is all together some kind of hacking. That means to reduce the entry barrierer down to zero and provide a space in which ordinary stranger can become sucessful. The problem for established academiia is, that this working habbit can become normal. This contradicts the normal story which is told inside of science.
The interesting aspect of Academia.edu, Unix and Wikipedia is, that the principle works. That means, it produces something useful. So the question is, why is serious science not open? Why is publishing only possible if someone is a member in IEEE? And indeed, answering the question is the problem. Or from the other way around, Wikipedia is something different from science. One the first hand, it has much in common, but Wikipedia works different. That is the reason, why so few professors are part of WIkipedia. They ignoring the website and they are in fear of it. It may look surprising, but the mathematics section in Wikipedia was not written by mathematicans at the university. The reason has to do with the different biographical background. That means, a mathematican according to the AMS society is somebody who has a phd degree and works since many years with a university background. That means, it is per definition not everybody, while in Wikipedia a mathematican can be everybody who is uploading an interesting artcle.