There has been some buzz for the past few days that Wikipedia is running out of editors. Actually, the original article was more about the shortage of admins, but whatever. It's old news to me. Whenever I make a change on Wikipedia, I always prepare to have to defend it. It used to be that any change would get immediately challenged and/or reverted, and you would have to spend a lot of time and effort defending it, citing sources and negotiating with other editors over the wording until a consensus was reached. Each article had its dedicated editors, ready to protect it from spurious changes, while others seemed to scan every change on Wikipedia and swoop in. Now, that rarely happens. After I make a change, I wait, and wait, expecting a battle, and nothing happens.
I think that a big reason is that Wikipedia is finished. Obviously it will never actually be finished, but in its early days, there were still lots of major subjects that lacked articles, and lots of articles which lacked much information. That is not nearly so much the case today, with over four million articles on the English version of Wikipedia, covering the most obscure of subjects. In fact, I think that many articles have too much information, being cluttered with a lot of insignificant details that can make the more important ones difficult to pick out. With so much information already there, there is little incentive to add anything.
Another reason that people don't want to edit Wikipedia is what I described above, that it has a reputation of being just too damned difficult. Anything you edit is likely to get reverted, and you have to be prepared to spend a lot of effort defending it. There have been plenty of stories about people trying to correct facts about themselves, and not being allowed to. Amateur editors have a reputation of being actually hostile towards experts trying to set facts straight. There also has been a slew of rules made that the casual users do not know about, and run afoul of anytime they try to make a correction. Nowadays, the dedicated editor's role is more that of curator, maintaining the fiercely fought consensus against the hoard of vandals and spammers. Aside from those with a stake in their personal fiefdoms, there is not much incentive in joining their ranks.
To be honest, sometimes it can be fun to do battle. I feel disappointed when nobody challenges my edits. Am I really that good that they cannot dispute me, or is there nobody left minding the store? I actually depend on other editors to keep me honest, by reviewing my edits and polishing off the rough edges. But even when they don't, that anticipation forces me to be more thorough, to post my sources and to refine my wording.
And if any n00b tries to change my edits, I put the hammer down on them!