I wouldn’t fault the manufacturer or vendor here. They tried and could not get people to wear it.
According to both the developer and a rep for the product, the weight of the EXO was what riders cited over and over again as the reason they wouldn’t wear it. They tried very hard to get a top UK pro to endorse it and wear it. The best they could do was Kitty King but she would only wear it on her younger horses and not her top (i.e., more visible horses). She said it was because it was too heavy - 8 lbs - and she ‘couldn’t do that to her owners’.
The range of sizes might have been limited at first but with success, this would have changed.
The company also faced significant opposition from other body protector manufacturers and due to this, British Eventing couldn’t endorse/recommend the product. The complaint from the foam vest companies was that the EXO was patent-protected and therefore they couldn’t compete.
The sad truth is eventers rejected a tool that could prevent death and serious injury.