Matthew and James the son of Zebedee were killed with a sword. Thaddaeus by arrows and James the brother of Jesus was stoned. Thomas was speared and John died of natural causes. It's true that a lot of people have died for a lie, but very few would die knowingly. That's harder to believe than the fact of the resurrection.
Sorrowful sadness turns to jubilant gladness.
A bad nightmare has been recast into a dream come true. Pessimistic hopelessness was changed to certainty. Optimistic hopefulness and skeptical disbelief in the resurrection is transformed into passionate belief that Jesus rose from the dead. The removal of the body from the grave could not account for this radical transform their spirits and characters. Three days is insufficient time for a legend to spring up.