Why can't NPCs use New-U respawners?

I've been somewhat curious about this..but.

Spoilers:

In Borderlands 2, Roland dies; shot and killed by Handsome Jack.

In this case, why couldn't he use the New-U respawn technology? In Borderlands 1, he was able to use it (in fact, all 4 of the original characters could do so), but in Borderlands 2, it seems like death is permanent, instead of being temporary.

What explains this?