I believe you also suffer from square-cube effects. Take a light airplane with a parachute, and scale up all the linear dimensions by a factor of two. You now have something with four times the drag (drag is proportional to cross section) but eight times the weight (weight is proportional to volume). That means your terminal velocity increases by 40% (proportional to the square root of mass/area). In short, if you take a system designed for a SR-22 and just scale it up for a 737, the jet would descend much faster under the canopy, probably to a degree that it would no longer be safe. The parachute would have to be proportionally much larger still.
And as you say, they wouldn't add much safety because there isn't much more to be had. I can only think of two large jet crashes offhand that would have potentially benefitted (the DC-10 that crashed in Sioux City, and that Japanese 747 where the tail fell off) and that's from a period of decades.
And as you say, they wouldn't add much safety because there isn't much more to be had. I can only think of two large jet crashes offhand that would have potentially benefitted (the DC-10 that crashed in Sioux City, and that Japanese 747 where the tail fell off) and that's from a period of decades.