I'm not going into the recent pagan origins of Easter here, but I would like to examine why Christians made up Easter in the first place. Very early in the Jesus traditions it was believed that Jesus was crucified. There was simply no way to get around the belief he was killed by the Romans. This gets very confusing from this point on. Jesus preached (I am conceding here that he was a historical person as his existence does not matter for this discussion) the "good news" that God would establish a real live kingdom in Jerusalem. There were many traditions within this tradition. What Christianity is today is Pauline. He taught a very different tradition that became many traditions. There was a cosmic spiritual battle in space and we were victims of it. Jesus was there to do spiritual not real physical stuff.
This was very convent and necessary. Jesus was now dead no getting around it. Jesus died because the Romans saw him as a threat that is all. There were many, many apocalyptic profits that died he was no exception. Paul changed the game by making it a spiritual thing that man could not have any effect on. It was Paul that made him into a Savior for the sou,l not the live body that would live in Jerusalem with god. With the bible we have a a great mixing of theses two major traditions along with traditions within these traditions. That is why it is so confusing concerning the idea of Heaven and related doctrines.
There were many demigods that were killed and resurrected in many traditions that had been around for many centuries. A dead prophet was not very impressive. A dead God would be even less impressive. So Jesus had to be resurrected just to keep up with the other God myths. But he of course had to be even better than them. Jesus actually became GOD. We can directly observe this transformation. In the book of Mark the first Gospel written,Jesus is a suffering man of God that doesn't even want to be there "take this cup from me" he says on the cross. 40-60 years later when the gospel of John was written the book starts out with the word(Jesus) was God, His last words on the cross become "it is finished". In Johns account Jesus is in control and actually making it all happen, as opposed to Mark where his is a victim.
For what ever reason even though the early Christians made up a resurrection story (bigger and better) they failed to come up with a back story to explain why he had to be resurrected. Christians still are in conflict about this today. The most common answer is that so we could all live forever. There is nothing in the bible to suggest anything. Now comes the sweet part. Jesus is not in the world doing anything at all. He wasn't then and isn't now. They had a story that he came back to life and was not anywhere. So obviously you have to now cover for his non existence. Naturally he goes to Heaven (the other heaven) and is never seen or heard from again. Modern Christians say that that is because he lives inside us. Don't hold your breath to see that manifest.
So in short there had to be a Easter story for the religion to progress and exist.