Whatever these positions were "meant for", the reality is that an ever larger share of classes are taught by people in these positions. Some of them are retired from other jobs; some are postdocs or working on the side; some are trying to cobble together a full time job. In many fields there is no "industry" from which to draw instructors.

No one is claiming these are research positions, but if universities are going to take teaching seriously, they have to address who is doing the bulk of the teaching.