One possibility is that stories of a resurrection could all too easily come about through a process of Chinese whispers where tales grew in the telling, set against the background of those times where the idea of resurrection was common.
I have a feeling that the Osiris story flourished in a setting that wasn't hostile to it.
But the Gospels are not so.
The Gospels grew, despite all attempts to squelch them before they even got started.
Saul of Tarsus being second to none in leading the way to vanquish Christianity before it ever got off the ground.
And as I said before, it would have been too easy to pwn the Gospels.
Just go get Jesus' body and put it on public display.
In addition, the Gospels contain acts of history that could have easily been verified.
I was born in 1954.
It is now 2021, about to be 2022.
If someone wrote a book that said, in 1956, Eisenhower ordered the deaths of all children 2 years old and under, and tomorrow I wanted to put an end to that lie, I would start going around to every church in America with my birth certificate showing that didn't happen.
I'd be going around saying, "If Eisenhower ordered my death, what am I doing here?"
In fact, multiple thousands of those born in 1954 could be going around exposing that author's lie.