Yes they do go down to just one water park for November through February. Typically TL is rehabbed (is that a word?) first in Nov and Dec, then they re-open that and close BB for Jan and Feb.
Obviously they do have to do rehab work on the parks, but I guess also they feel there are only enough guests to warrant one park being open during off season. Plus with the weather not guaranteed to be hot, it'll drop attendance too.