Maybe it's structural?
Once that cavity has been put in, you're essentially leaving not a great deal of wood at the face of the guitar to which you can attach a hard tail. The string tension may warp the body if there's not enough wood to anchor the bridge into? and since changing bridge position would alter the scale length, then you're really stuck with the same relative position on any strat body?
i'm just guessing that's why once the cavity has been routed it has to get a trem.
but i agree, that being a non trem kinda guy it'd be nice to see more hard tail strats/soloists/VIPs in the showcase.