As for being a demon, I will not tell. I think to myself as a master manipulator and holding back information is a great way to manipulate people. Also, such information is a great advantage in many situation, I will like to keep my advantage for now.
Hmmm. From what I understand in psychology, creatures want another creature dead if they fear it or feel that the creature is a danger to them (to their health, power, wealth, sanity), like how humans kill snakes and spiders (they fear them). You might be, from being nosy it seems, gathered knowledge that other demons don’t want to share with others. They fear that you might divulge it to others. Getting rid of you is a great way to do that, though they might not feel it urgently since it seems you aren’t spreading those (except is certain cases like pointing out Bess to Tom as being a demon even if she is in her disguise).
There is also those who love to kill and/or hunt but it doesn’t seem to apply to your situation.
Also, if there was a proof about the effect of the compulsion on the demons, then the ‘purge’ that is done on the city is a mighty proof. Tom isn’t able to withstand it. The archdemons isn’t also. I was also trying to see if the ‘purge’s’ effect correlates to the power of the demon. That is the weaker the demon, the stronger and faster the effect of the spell will be. It seems so. The weaker ones are the ones who fled first and the stronger ones last. Of course there is a margin of error. Some weaker demons might stay longer due to circumstances or will alone, and the stronger ones might just fled even if the compulsion is not that strong enough (like the case of Tom).