Why don't commercial jet aircraft have a break-apart, parachute escape system?
wouldnt that work for keeping a majority of passenger jets from crashing?


The majority of passenger jets don't crash.

Designing an aircraft like that would incur very substantial weight penalties. The Space Shuttle booster rocket parachutes weight 990kg, each (it needs 3) plus 550 kg for the drogue chute needed to pull out the main canopies. Plus another to pull out the 550kg drogue. Where are you going to put that much nylon?

Then there's regular maintenance of stuff that large and heavy - you will need an entire empty hangar to repack things along with a crew and a crane.

Also consider how you are going to break up a commercial airliner in an orderly manner. It would have to be designed for it and lined with explosives. That's going to be really popular.

Finally, parachutes need time to work. Large parachutes need considerable time. So this whole process only helps if there's a problem in cruise flight, and that's the phase with the lowest accident rate. Parachutes below 1000 feet are just excess weight.

Semi-related Addendum: After Challenger went boom the Space Shuttles were fitted with a crew escape system. It was intended to allow the crew to exit when the craft was under control but unable to reach a survivable landing site. Re-read that carefully: when the craft was under control. The crew exits at reasonable altitudes and the Shuttle crashes under remote control.

Parachutes simply haven't been a viable option for commercial air transportation since the DC-3 era.