“At the Rema’s time, an Ashkenazi community in E”Y (had such a thing existed) also would not have Duchaned daily.”
That’s because “minhag avoteinu”; whatever they did in Europe, they continued to do in E”Y. The reason why most Ashkenazim duchan daily in E”Y is because most of the founders of the Askenazi yishuvim were tamidei haGR”A. As pointed out above, in Haifa and in the Galil, they don’t duchan daily – not talmidai haGRA.
In any event, I interpret the implicit question of why don’t Ashkenazim duchan daily as saying what caused them to stop. Clearly the practice in E”Y was more often than just Y”T (see Sotah 38b towards the top and Rashi 'Liperakim' - 10 lines down). The Rama addresses the question, but his reasoning is not based on what happened in his time, but rather on what caused them to stop centuries before. Many read into his reasoning to include the difference of chu”l was part of the reason.
