Having perfected the art of trafficator removal and repair, based upon my doing it 20 times before I got it right, I feel comfortable speaking on this subject.
First, as said above, they only return on turns of 90 or so, and soft turns aren't sufficient to reset the trafficator. Now if that's not your problem, the answer is in the trafficator return tabs, which are probably either bent or a little worn so that they don't make sufficient contact with these itty bitty little metal things that stick slightly out of the bottom of the trafficator. These are technical terms, so pay careful attention.
If that's the case, you won't have to actually dismantel the trafficator to find out. By loosing the 3 nuts at the wheel hub, and giving yourself some slack at the bottom of the steering shaft, you can pull it out enough to either slightly bend the tabs upwards to improve contact or, if you want to try something a little easier, wrap a single piece of electrical tape around the tabs to increase their depth and improve contact. Then put everything back, take it for a spin and watch your tafficator closely.
Then repeat 19 more times, as you realize each itty bitty little thing that was slightly out of place, whack, missing, broken or whatever. Eventually, you get really good at this.