Typically, there is only one reason any aircraft is fitted with a stick pusher - the type cannot be shown to comply with the stall handling characteristics requirements of the applicable certification standard without it.
The stall handling deficiencies may included, deep stalling, unacceptable longitudinal handling or stability on the stall approach, unacceptable levels of "roll off" at the stall.
While, often, unacceptable characteristics may be corrected with aerodynamic fixes, that may be the more expensive option. It may be cheaper just to fit a known acceptable stick pusher system than to embark on a stall development programme with an uncertain outcome. Also, the aerodynamic fix may result in an unacceptable increase in stall speeds from a performance viewpoint.