I see why many people consider this to be a problem, and it does severely limit the ability of knowledge to persist, but I think there are some benefits to it, namely that the answers can always be up-to-date.

I don't know how many times I've found answers for versions of my libraries/toolkits that are so old that they're useless. There's little point these days in persisting answers to questions about Node 0.4.0, for example - and that's only ~7 years old, downright modern by some viewpoints.