really? When did you last have an engine failure? or any in-flight unexpected event? Perhaps you're extremely fast in your thinking, evaluation, and reactions, but studies show 3 seconds is closer to the mark, when you include the time required for the "what exactly is happening?", "is this really happening to me?" and "what do I do next?" thought processes. It's not just the reaction time. My own experience supports this.
The point is, if the jetpack engine stops, the pilot's mind has to go through multiple steps before he/she pulls the lever that operates the ballistic chute.
Hopefully, of course, I'm completely wrong, and no-one flying one of these has any such calamity befall them.