In my region, during the early 1970s, 3 speed IGH were a good seller for the 30+ crowd. They wanted to get involved in the new bicycle culture but were intimidated by derailleur systems and wanted something with an upright riding position. Consequently, they gravitated to the more familiar 3 speed, middleweight bicycle, which is what we called bicycles with 26" wheels.
The big 3 speed middleweight seller was the CCM Elan, as it was Canadian made and inexpensive. The 30+ crowd still believed in Made in Canada, whereas the under 30 crowd had no allegiance. My recollection is that the Elan was CCM's 2nd biggest seller after the Targa, which was the base 10 speed model. However, you find more surviving Elan, as they were ridden less and rec'd better care, both of which were 30+ traits. The Elan was available in men's 21" and 23" frames, along with a 20" mixte. These bicycles, with their instantly recognizable olive green paint, surface regularly in local classified advertisements.