@Highflyer1 since we live in the physical world, nothing is 100%. There is a finite probability that any safety mechanism will fail to operate when it should, or will prematurely operate when it should not. This is true for car airbags, seat belt retainers, anti-lock brakes, jump standard safety cups, XC obstacle MIMS clips, and riding air vests. For safety mechanisms which are advanced with a lot of field and lab experience, those probabilities of failure to operate, and premature activation are low, but still not zero. Society has deemed them to be acceptably low, even though the incorrect operation may cause a death.
The 2005 Univ of Georgia airbag statistical study showed that they appear to cause more deaths than the NHTSA was indicating. The 2015 study by Takata (air bag company) showed a remarkably high rate of failure.
The point is that society generally thinks they are reliably, without question, even though they are not as good as is assumed. However, we are no where near that level of reliability and prevention of injuries with equestrian safety air vests.