Well, first, it is used in hundreds of medieval profiles here, and assigning the other dozen helps to find duplicates. Second, we have thousands of Holland's here too, which is not an official LNAB either.
In other words, we have a practical situation here, where loads of profiles with an LNAB like Franken or Holland exist, even though these are not official LNAB's. And for me, Holland is a geographic area, just like Hainaut, which is official here.
Anyway, if Franken's can be reassigned to a house like those mentioned on the Franks wiki page, there is no reason to add it as an official LNAB. But until they really are reassigned, those hundreds of medieval Franken profiles are still there.