Of course it would be better to have an FDR on all aircraft but you have to be practical and the CAA would have more reason to insist on an FDR on passenger carrying commercial aircraft as opposed to private aircraft.
A couple of other Citation 1 accidents have already been mentioned where it would have been invaluable to have an FDR on board. Cost? What price the safety of all Citations? If you have an aircraft worth several million dollars an FDR is not going to break your bank account. If you have an old version then you are going to spend a lot on parts anyway as they wear out. You have to be prepared to sink a fair amount of money into the aircraft anyway. Why not fit an FDR? If it were mandatory I am sure you can convince your accountant.
One reason why commercial airlines are so safe is the information learned over many years of operating them and from incidents and accidents that have happened with the aircraft becoming better designed with that knowledge.