Discussion of this particular forum aside, there are very good reasons not to evaluate the existence/continuance of forums based only on post metrics.

1. FT is primarily a library of information. Any library needs a good cataloguing scheme. Some areas will have few "books" but need to exist nonetheless for the sake of orderliness. (Analogy -- which are always tricky -- suppose a library has few books on, say, the raising of ferrets. It makes no sense to simply say, "Well, our library won't have that category anymore and we'll just put any such books in some random place.") Which leads to #2:

2. If I were a first-timer to FT, having heard that it is a great resource for Travel Information and wanted to look for information about, say, the Atlanta airport, it would never occur to me to look in an airline forum for that information. If FT is going to advertise having four very broad classifications of information, then the information needs to be filed appropriately. This may mean that some forums that are little trafficked are available nonetheles for those who are looking for information or asking questions. (Where would questions about Antarctica go if there weren't a forum for it?)

3. Some forums simply are an asset to FT and a point of pride, whatever their traffic metrics, and FT's making them available is a good thing. Having a respectful, non-misogynistic Women's Travel forum (even if it's post count were to drop significantly) is something FT ought to maintain because it's the right thing to do and adds luster to the brand.

Forum traffic metrics are an index of forum use, but forum use cannot and should not be the only criterion for whether a forum exists.