okay, so.
think of the devils bargain like this...
you can get protection (which is good mayyyyybe on late game if your role is strong)
you can kill someone (which is good if you know someone worth attacking)
or you can trade your role (which is good if you dont care if the devil knows it, ie, youre not a strong role... like journalist or citizen)
so, with this.... protecting yourself early game is sort of a waste cuz you dont know where the attacks are going to go. so its basically giving the hell team a free soul.
attacking is mostly only useful for the wolves or other evils, since its easier to hit town than evils.
both of those things give souls for a potential wasted ability use. which in turn helps the devil protect themselves.
then trading roles is fine if you dont care about them knowing your role, it also gives you info about another (and also gives them that info)
but this doesnt give them a soul, so thats okay.