It could just be a difference between theoretical and realized niche- i.e., they can survive just fine in a broader range of conditions than they actually occur in in the wild, due to some combination of history, competition, sublethal effects on fitness, etc.
I have often wondered the same about this species. Sort of like how pitcher plants (Sarracenia) don't really need a low nutrient environment and bald cypress (Taxodium) don't really need standing water to thrive. They just don't compete well in those settings.
As an interesting aside, Sarracenia will stop making trumpets if there are sufficient nutrients, and only make phyllodia.
NANFA Youtube Channel 
