I suspect the reason for this is that Cajun cooking, for all its glorious flavor, is not much on looks. Much of it is pot food from very big pots. More of all of them in both Creole and Cajun than in most other cooking styles, but more than there used to be in both. You can pick on a few dishes. Creole jambalaya tends to be reddened with tomato, while Cajun jambalaya tends to be brown and lack tomato.
Gumbo is smokier in Cajun country than in New Orleans.
But you do see oysters Rockefeller in Lafayette, and crawfish etouffee in New Orleans. There's been so much cross-fertilization of the styles over the decades that the merger has been consummated. I say, stop thinking about it. Just eat it. The best job of dressing up the traditional Cajun dishes for restaurant service without losing their long-cooked soul.