An interesting part of this is that Carnivorous plants belong mainly to two evolutive lineages. To simplify it, a main group is distantly related with Rosmarinus and Olive trees and the other main group is a distant cousin of Pinks and Cacti.

This introduces a totally different group of carnivorous in the order Saxifragales, that includes Blackcurrants, Peonies and Aloe (sometimes people confuse Aloe with a cacti, but Succulents aren't cacti).

So the plants became carnivorous at least three times to adapt to specially hard places, and they need very humid places to do it.