Beags,
Because SWB VOR is a 'terminal' rather than 'en route' beacon (I've heard that as an excuse)? Playing around with that NATS app, it doesn't seem to recognise either the BZ or LA NDBs, or any of the TACANs, so maybe it's a Mil vs. Civil thing... I know you can't use ICAO references for airfields (if you insist on planning through airfield overheads).