re stick "nudgers" and stick pushers
Stick pushers are sometimes fitted when there are "stability issues approaching the stall" - in such a case, though, in order to fix such issues the pusher needs to be set to trigger BEFORE the adverse characteristics are manifest, with attendant likely adverse impact on stall speeds. A pusher can also sometimes be fitted when the characteristics AT the aerodynamic stall are acceptable, but the post-aerodynamic stall characteristics degrade so quickly that a "barrier" is required to prevent excursions into an unsafe zone. Bottom line, pushers can be fitted for a variety of reasons.
Regarding why no "nudger" was fitted and MCAS adopted instead: A "nudger" would operate on the elevator, not the stab. If the issue is insufficient elevator authority/power to dependably recover from a stall under worst case conditions, nudging the stick will achieve nothing. In such a case, the solution is either more elevator authority (major redesign) for "help the elevator with the stab". The latter seems to be the MCAS solution.