There are many reasons. However, I will just focus on one set of reasons. The only way to explain the growth of the Christian Faith in the very place that the crucifixion took place is by the resurrection. If the resurrection hadn't taken place, no one would have believed:
The Apostles had all abandoned their faith and were on the run. Their faith was only renewed by Jesus' post-resurrection appearances.
Many who hadn't previously believed subsequently came to faith, like Jesus' family. They couldn't possibly have believed after the cross had there not been a great miracle of the resurrection to have changed their mind.
Many of the religious leadership of Jerusalem came to believe. Had there been evidence contrary to the resurrection, it would have been available to them there in Jerusalem, the very place Jesus had been crucified. They, therefore, would never have believed and risked both life and career.
In fact, thousands came to faith almost immediately there in Jerusalem. There must have been sufficient evidence for them to have done so.
Had there not been a resurrection, there could not have been a Christian Faith. Jesus had suffered the most dishonoring and humiliating death. No one would have wanted to have been associated with it.