Part of the problem here is related to how you make a finding of negligence. The airfield operator alleged to be at fault will be measured against the mythical "reasonable" airfield operator. Inevitably, that involves looking at what other airfield operators do in determining whether a particular operator took or did not take enough precautions to protect people who use the airfield from harm. While no other airfield operators were using high-viz vests, then the standard of care required from an ordinary airfield operator probably didn't extend to the wearing of high-viz vests. As they become more widespread, maybe the "reasonable" operator would have used them so the standard changes.
At the end of the day though, its their airfield, they can make you wear bright pink bikinis if they want and if you want to use the airfield. If the operator is a public body and took that decision because it has a thing for bright pink bikinis (rather than on safety grounds), maybe you can get judicial review if you felt so inclined (cheaper to buy a vest though
). But for a private airfield operator, your remedy is not to go there.