If StackOverflow is a wiki, then the best answer to a question should be determined by the community, not the asker, and needs to be able to evolve and change over time.
However, StackOverflow simultaneously insists questions can't be duplicated while making answer selection immutable and controlled by the asker. This results in a suboptimal experience.
Here is an example question highlighting this: https://stackoverflow.com/questions/884177/how-can-i-determi...
I currently have the best answer to the question "How can I determine what font a browser is actually using to render some text?". The answer I gave was the best answer in 2010. Things have changed a lot since then, and my answer is no longer the best one on that page.
_But no one can change the best answer, which is insane!_ As a result, you see best answers to old questions being turned into community wikis edited to include better answers in the thread, rather than those answers being selected.