why do passiflora flowers only last a few days?

Now thats a good question ....the answer is the plant has such a short flowering period that it has to grow at an enormous rate so energy is vital ...by flowering and shedding in 24 hours it gives itself a chance of survival....by the way only the infertile pods will fall to the ground....if you find that the fruit is falling before its ripe then you have a problem.
hope this helps
Best Wishes
Kev