I think forum platforms are still the best type of web site for communities that need to communicate in the long term, i.e. where information does not get stale quickly.

For instance, in building-hobby/crafting forums, people post threads about their ongoing projects, which sometimes may take years to complete.

In some collecting forums, there are threads that are over a decade old — and still active, each with a wealth of information about one very specific subject. Disagreements about details about a specific type of item means that there is sometimes a lot of info that can't always be easily collected into a wiki.

However, these forums are dependent on there being a good search function: When they breaks down, people do complain. It is also not suitable to automatically lock/cull old threads on these forums.