It’s not like there was a “Paris of the…” certification process. If Detroit was, it was well before my first visit 50 years ago. As another commenter alluded to, it is an aspirational marketing phrase. Like how Redmond, WA claims to be the “bicycle capital of the Northwest” without having a single protected bike lane.
I think there was ~13 major auto factories in Detroit at one point, and what would happen is when the UAW would protest, they'd leave one factory and go to another, more important factory (often wherever they were producing engines) to apply pressure. The result is auto makers were forced to build new factories outside of Detroit, first in other MI cities and eventually in other states and countries. Now I think there's only ~three factories in Detroit, including for products that aren't really that exciting like spark plugs.
I didn't realize so many cities were referred to as an american Paris though, that is interesting. It was, certainly however, a beautiful city at one point.
Interesting. I heard that Detroit was known as the Paris of the West. Looking it up, it seems this was a fairly common phrase applied to many cities over the years. [0]
Detroit also has had $1 homes, but as with everywhere else, that isn’t the end of the story.
[0] https://en.m.wikipedia.org/wiki/Paris_of_the_West