Most likely they're probably feared. A device that brings people back from the dead, humans would kill you if they even suspected you could have one/make one. Humans fear what they don't understand. So the device was probably banned, and made illegal. There were only 1000 made anyways (I'm pretty sure), and they're all keyed to the individuals DNA. So even if they got their hands on one, they wouldn't be able to replicate the effect.
In the end, humans are just morons.