The challenge for any private company is that the solution needs to be completely integrated into both the device and behavioral patterns need to be re-learned. For most people (in the US), calling 9-11 has been engrained since they were a child. In a moment of panic, it's the first or second reaction... not loading a 3rd party app. While not impossible, convincing Apple or Google to let you own "SOS+" capabilities would be a tall order...
Spot has succeed in the adventure market by owning the device and behavior change being easy to manage with no cell service. Just about everyone I know who has a mountain home, sailboat, or frequently travels to remote places – has purchased Spot.
If I was a VC, I would be interested in a roll-up strategy... GEOS and Spot aren't the only solutions.