Rope wicks have been used for decades in masonry wall assemblies. Why are they frowned upon in modern masonry walls?
There are a few different stories about the history of rope wicks.  An old training book we have in the office from 1924 explains that rope wicks were to be removed to leave a weep hole. Cotton rope wicks eventually petrify when moisture transports cement and sand fines into the rope. This hardening of a rope wick negatively impacts drainage efficiency.  Modern masonry wall assemblies are designed to be drained and back-ventilated rainscreen walls.  The purpose of a weep vent is to allow moisture out of the wall cavity and air into it.  Rope wicks do not let air into the wall cavity.