Because life is grey. Pilot skill level varies. Situations vary. Being over a paved runway is different than being over rugged mountains. The attitude of Cirrus seems to be that BRS is one more thing for the pilot to consider based on his particular situation. As data from its use has built up I will say more and more members of COPA (where this is heavily discussed) are leaning towards pulling if it will be off airport. Why are you insisting that the manufacturer tell you what to do as a pilot?
+1... Cirrus should only specify the data on when the parachute will come out, and the descent rate. Things that you can take into account when deciding on your course of action.
The other thing people talk about here is the shame of destroying a perfectly good aircraft. What proportion of forced landings result in the destruction of the aircraft, I wonder?
I get the impression that quite a high proportion of forced landings destroy the aircraft even if the pilot can walk away. At least a few cirruses have been refurbished after accidents.