Why on Earth would I want to contribute to a wiki

From Wikipedia

There are many good reasons to be involved in Wikipedia:

It's fun.
It's easy.
It's educational.
It's social.
You can correct other people on the spot without asking their permission!
It's exciting. Wikipedia has created literally thousands of articles in the mere months since its inception--over 2,000 per month, in fact.
It's interesting to share your knowledge with other people, particularly knowing that others can instantly edit or react to what you've written.