Parachutes require pretty specific conditions to be able to use, and they require a fair amount of know-how. Expecting random passengers to be able to operate a parachute at all is basically a losing battle, and if you had people jumping out of planes that were on their way down, you’d have a lot more people dying (speculation but I’d wager money on it) than if they just stayed in the plane. Plus it’d be a horrible look for the airline - even worse than a plane crashing and killing everyone on it - if they had dead people raining down over cities and whatnot because they jumped and didn’t properly deploy their chute, or deployed it too quickly, or didn’t jump at the right time and got hit by the plane or any number of other possible problems.
Fighter jets and the like have ejection seats that specifically propel the pilot away from the plane before deploying the chute, and recreational (or military) planes that people are jumping from are designed for that purpose, and are moving a lot slower than commercial airliners. Opening the door on a plane to let people jump would cause more problems than keeping them on the plane. (People getting sucked out the door and the like.) Getting passengers safely clear of a plane that’s going down unrecoverably would be basically impossible.
Commercial airlines also fly really high up. If you were ejected at cruising altitude, the first thing you would do is pass out and fall for a few minutes. Hopefully you wake up in time to orient yourself and activate a parachute.
That’s not to say you couldn’t have an auto deploy mechanism at a given altitude. I haven’t skydived (skydove?) in years, but isn’t there an emergency deployment mechanism if the chute hasn’t deployed by a certain altitude?
There probably is, but that brings in another huge problem. Maintenance of all this stuff, parachutes can’t just stay packed indefinitely. Maintaining 100s of parachutes per plane is wildly impractical.
I know absolutely nothing about this, but aren’t there parachutes that basically just auto-deploy as soon as you jump? I seem to remember seeing something where people hop out and are followed out by a long piece of string that catches on the plane and yanks the chute when it hits a certain length, or something like that. Presumably they don’t work at 11km elevation though.
https://en.wikipedia.org/wiki/Nick_Piantanida
This guy was in a remote controlled, parachute equipped gondola at 17km altitude wearing a pressurized suite. His suit broke and even though the emergency descent of the gondola was immediately activated to descend safely, he later died from embolism (bubbles forming in the blood because of rapidly decreasing pressure). Passenger jets cruise at about 11km so i gather it would be similar.