A FH static fire can only be done on the pad: there is no test stand big enough to do it.
* staggered start, the engines are started in pairs on the order of 100s milliseconds apart, so 13 chances for an unbalanced engine start
* vastly increased acoustic and vibration shock, I really wish I could hear the noise in person (from a long way away)
And the Engadget article just references an aviation week article (paywalled)
There's a lot more (non paywalled) information here:
This made me laugh. I think it belongs on shitelonsays.com.
Yeah, I doubt it was seriously considered. Probably just didn't want to tell the Air Force what they were really planning to use the Raptor for. Can't say I blame them!