[mikeash]

Technology to record the full flight is, of course, easy. Storage is cheap these days.

Except that if you want it to be a useful back box, it needs to survive Events. Like being blown up in midair. Or roasting in a jet fuel fire for half an hour. Or, random example, sitting at the bottom of the ocean for several years.

That multiplies the engineering challenge, which in turn reduces the amount of storage you can put into the thing.