- To jump out, they would need to open the doors. There would be problems with decompression at above 10K.
- You have to deal with people unable to use parachutes. Children, elderly, disabled, afraid of heights, and panicked.
- There’s an assumption an airplane remains level enough. If it’s spinning or nose down, trying to reach an exit is another problem.
- If jumping out ahead of the wing, there’s a risk of getting sucked into the engines.
- Parqchutes are bulky. Trying to get them out of storage and distribute them to a couple hundred untrained people is a tall order.
- Putting on a parachute, correclty strapping it, knowing when and where to pull the cord, and knowing how to land without breaking bones, hitting tree branches, or ditching into water. These are all issues you can’t teach during preflight safety instruction.
Overall, everyone would be better off staying put, not panicking, and hoping a plane and trained pilots can get everyone on the ground, safely.
Building them into the seats makes about all those problems go away. But decreases the amount of seats you can fit on plane and amount of money made per flight and therefore is never going to happen
If a plane can stay level enough for long enough to get people into parachute gear and out the door, chances are good that the pilots can land that plane, which significantly decreases the chances of injury to the passengers.
That’s my thought - there would be very few instances where a parachute for the passengers would potentially be useful. Either there would be no time or opportunity to strap on a parachute and bail from the plane, or they would be better off staying in the plane for some sort of emergency landing.
Something like United Airlines Flight 232 (loss of hydraulic pressure resulting in no control surfaces) is one of the few exceptions I can think of where having a parachute might be useful. In that case the pilots had enough control of the plane that the passengers would have had an opportunity to bail, and that would have been preferable to trying to ride out a landing.