In addition to the benefits of proving liability, would those drivers drive better themselves, knowing their actions can be held to account, as well as the other party (if there even was one)?
It could pay off twice for insurance companies to hand them out, as it would help them prove liability, and might make their customers better drivers too?
That said ....... watching YouTube I'm well aware that sometimes owning a dash cam can have the complete opposite effect. Plenty of dash cam owners refuse to yield to avoid incidents, and purposely involve themselves in totally avoidable accidents knowing their camera proves them (legally) faultless