Well, more specifically, why airlines won't install this device unless they're made to do it... and they won't.
If you were Malaysian Airlines right now you might wish you had one of these devices installed on the plane because it would resolve much of the public relations headache they are currently facing by letting them know NOW what was happening to that plane before it disappeared.. But that's about all it would save them. It won't save them anything else.
An airline is only going to want to install such a device if it directly benefits them financially and this device offers very little.
I doubt the FAA is going to require US carriers to install it because it offers very little the black boxes don't offer. It doesn't happen very often that a black box is unreadable or unrecoverable after a crash. It happens, but probably not often enough for installation of this device to be worth the cost and the trouble, especially that when those boxes are unavailable investigators have almost always been able to figure out what went wrong by using other evidence.