After 11 edits (12 versions) from the same user an answer becomes community wiki. There are lots of questions regarding the way in which this happens but none (that I could find) regarding "Why". And humans hate not to know why!
Most other reasons for community wikification make obvious sense; if a post has been edited by many many users it doesn't really belong to anyone anymore. But the 11 edits creates a perverse incentive not to edit your own posts to perfect them. Previously I would return many times (possibly weeks after I'd posted) to improve a big answer but I basically don't do that anymore unless I can remember exactly how many times I've edited before or now that I'm not completely new to the site, look at the "edited" link and see that I still have several edits left.
That's the reasons against this system, but I'm presuming there are reasons for 11 self edits leading to community wikification, which brings me back to why?
This question refers to a behaviour which no longer exists. Posts are no longer automatically converted to community wiki