Why are partial protected sprinkler areas not more widely promoted

Why does the building codes and AHJ's not promote the use of partial sprinkler protection in basements , Janitors closets, storage rooms, furnace rooms etc.
The1-2 heads are tapped directly from the domestic water source no complicated expensive work involved.
High risk areas are covered with out the cost of deploying a full system. The use of these single heads and a full Fire Alarm System can provide more than adequate protection in many structures where a full sprinkler system is not really needed or can not be afforded.
Community's around me before the codes changed encouraged this practice and in fact several times these single head systems helped stop major problems and or gave occupants time to escape.
Your talking $20.00-$50.00 a head to do this depending if you your hiring some one or can DIY it.
But as usual no only full complete systems never promote a very cost efficient system which can be used in any home or business and easily retrofitted. At one time they even sold a kit you attached to your laundry sink and then hung the head above laundry equipment. But you know dam well UL and NFPA would have no such item on the market.