Ramana Maharishi said to his disciple pointing to a person nearby "Hey Muruganar! this person has to submit all his Japa to his Guru daily. How is that Guru?" to which Muruganar replied "that Guru is better. What to speak of this one who leaves not even the person" meaning that the Maharishi swallows the Ego completely.
Ravana had done a unpardonable act of lifting Sita. Instead of killing Ravana at once, which He is capable of, Rama delays the inevitable decision of killing Ravana.
In the process He annhilates Ravana's ego not in full but partially & that is a pain to Ravana's Ego. (Do not we see in films, where a villain often begs - kill me instantly - do not torture me?). If only there is a friend for Ravana's mind, it would have said "Rama, people say you are compassionate. But you have not been so atleast so far". Ravana got killed after a year after tasting bitter after bitter experiences fooled by both his mind and by Rama. Even in battle Ravana had to wait for 18long days. That is Rama. Take your time - I wait - so to say!
More or less, same, is the case with Hiranyakasipu. He had to hung his head in shame before his own men. Narasimma even without a appearance had done to Hiranyakasipu what Rama did with appearance to Ravana. Pulling the plug on Hiranya's ego. That is Narasimma. You play till i come - but then even there i dictate the terms - similar to that.
The Ego was made to suffer before Ravana or Hiranya were killed. To an extent, it is the case with Sisupala too. But better.
That was not the case with Tripurasuras. They flourished till at a time, they were killed by Siva's smile in an instance.
Siva at times have graced the demons, nurturing the Ego. He gives long life to Ravana. But then He turns up against him at an inopportune moment. I am neutral - behave yourself - that seems to be Siva's way.