Doc Marten’s is a small niche. I wasn’t in a wealthy town, but growing up everyone wanted one since they were a fad at that time. The crocs just don’t fit a niche.
I think the Crocs were slightly different than Doc Martens, as the Doc Martens primary appeal was their counter culture attitude. As such, people in the mall were good candidates for Crocs, but not for Doc Martens.
The Doc Martens were originally popularized by the skinheads because they resembled the boots Nazis wore in WWII. I know a lot of the kids were convinced that Doc Martens was the company that made the Nazi boots. That's untrue, although the founder of Doc Martens, Dr. Klaus Maertens, was a Nazi in WWII.