For the Muslim to convert to Christianity is from their point of view to descend to a lower level. Islam came after Christ. Islam has a later and higher revelation. Who wants to go back from the latest and highest to an earlier and lower? A convert from Islam is a traitor in the eyes of Muslims. As far as Muslims are concerned, such a person has died morally and the entire Muslim neighbourhood works together towards his reversion under the weight of contempt and of social deprivation.