As a vine, Carignan has a host of disadvantages. It ripens late so can be successfully grown only in relatively warm climates. It is also susceptible to both powdery mildew and downy mildew and needs extensive spraying in all but the driest climates. It is not suitable for mechanical harvesting because its stalks are particularly tough.
As a wine, Carignan can be pretty tough too. The wine produced is typically high in rough tannins and acidity and in southern France the softening vinification method of carbonic maceration routinely has to be used to ensure that wines made from Carignan can be drunk reasonably young.
With 6,000 acres planted, Carignan is still the 10th most planted red wine grape in California, but in France the real sea change came in the 1990s when, thanks to heavy financial inducements, southern French growers ripped out Carignan in favour of more fashionable "improving" varieties or other crops entirely. I can see why the appellation authorities have steadily reduced the proportion of Carignane allowed in wines such as Minervois, Corbieres, Fitou, Faugeres, St. Chinian and Coteaux du Languedoc in favor of gentler, fruitier grapes such as Syrah, Grenache, Mourvedre and Cinsault.
And yet, there are wines made almost exclusively from Carignan that are very impressive. Some of the most obvious are grown not in France but over the Spanish border on the distinctive brown schists of Priorat in Catalonia.