You've hit on my main reason for avoiding carbon fiber in critical parts. There is no practical, reliable, non-destructive test for carbon structures. They have to be built correctly, and then it becomes almost a matter of faith that they'll hold up if not stressed beyond the design limits.

For me that's OK for aircraft because there are good protocols in place. Likewise many builders of CF bikes a d forks have equally good protocols, but I won't accept on faith that all do. Then there's the issue of stress. CF forks may be fine for racing where equipment is treated with some care, and replaced on a regular basis. But I'm not sure about the real world where bikes often get little or no maintenance and where some ride road bikes as if they were Range Rovers.

I take decent care of my equipment, but all of my bikes have been involved in crashes, or had serious run ins with water filled potholes bad enough to dent a front wheel. I'm sure a carbon fork would survive that, but unwilling to then face the decision of replacing it, or wondering about it the next time I'm descending a bumpy road at a good clip.

BTW- this shouldn't be read as an indictment of CF forks as dangerous. The experience so far shows that they aren't. If I were racing and the lower weight mattered I'd likely be another user of CF forks, but I'm not so I don't. For my purposes, for the way I ride, and for the amount of time I keep a bike, the feeling of security that an overbuilt steel steerer offers is worth the weight penalty. (to me)