General rule is that Sportives are all laid out on a plate, kind of the roadie equivalent of a trail centre – follow the waymarkers, come back home for tea and medals and a freebie. You're paying for the bells and whistles, the electronic timing, marshals and full route marking, broom wagon etc.
Audax is sort of like cycle orienteering in some ways, much cheaper, much more self reliance, it's up to the rider to find the route and get to the checkpoint within a certain time window. There are often minimum and maximum average speeds imposed so you can't go balls out or you get there too early and get penalised! Checkpoints are often in cafes so that's your food stop sorted. 🙂