As I understand it, UX.SE is a site for collecting good answers to interesting questions, and less a site for rambling discussions in response to questions.
The "pick a best answer" mechanic drives somewhat towards the goal of getting good answers but often there are multiple answers to a question, each good in their part, but none which is comprehensive.
Contributors can update and edit their previously supplied answers but often don't. It appears that contributors add their two bits, and then let the next person add their two bits, but most contributors don't actively work on updating their answers to remain a contender for "best answer".
Is this the state of affairs we want as the status quo, or could we do more to encourage curation of answers?