Why did the great miracles like raising the dead cease after the death of the Apostles?

I would not say they ceased to exist. There are saints who, as the stories go, raised people from the dead, though that does not happen often, and to be canonized a saint you had to have at least three attested miracles with no natural explanation, so we have hundreds of saints who each performed miracles after the Apostles. What is not possible after the Apostles, John being the last, is new general, inspired, inerrant revelation: there will be no more books of the Bible, the Apocalypse was the last, and we now have all the public revelation we are going to get. So if someone comes and says God spoke to him, understand that God already gave us all the general revelation; what that person is claiming is a private revelation, that God made him an exception with a vision or locution. The way we handle that is to check whether he is legitimate: if it is serious enough, it goes to the local bishop, who, because he receives many such claims that turn out to be duds, will set up a task force and act as a devil's advocate to try to refute it. If it passes muster, it is recorded in Catholic history as a genuine private revelation, though people may pay it little attention, as they barely attend even to Fatima. So miracles did not cease; only public revelation closed.