Most electronic devices being banned on certain U.S.-bound flights

As any engineer can tell you, L-Ion batteries aren't hard to make into incendiary devices. Just need to break the barrier between the cathode and anode, then wait - 10-60 seconds. Build quality has been fairly good for most devices, so this doesn't happen accidentally very often, but there are lots of online videos which show what happens - it is fun to watch, if you are far enough away. Think they burn really hot too - 1,110 degrees F (600 degrees C).

Even a camera battery can put on a good show.

In the cabin, at least someone would see it, assuming the goal wasn't to have 5 of them going off in different parts of the aircraft to aid in the confusion.

Pretty much anything can be a weapon, in the wrong hands.

Why not make special containers that all electronic devices have to be put into in mass volume that in case one blows, no harm comes to the plane?

Looks like it is more about security than safety.

This flies in the face of recent advice that your L-Ion batteries are equally likely to be crushed or bent when your check-in baggage is tossed around by stressed baggage handlers. Better to have them close at hand where you can spot a smoking battery in the worst case scenario.