This is all pure speculation.
Every once in a while, one of my atheist or spiritual but not religious friends will post an article quoting one scholar or another about how Jesus was unlikely to have been a historical figure. I seldom get involved in the subsequent thread, but will often follow it for a bit, see where it goes.
Now, I feel like I need to say upfront that I'm not one of those Christians that feels like he has to defend every little question about my religion. If it were possible to provide incontrovertible evidence that Mary, Joseph, Jesus and the 12 disciples were all pure works of fiction, I don't know what difference that would make to me at this point. I recognize that a lot of the gospel story is a mythologizing of . . . someone? I've read enough "historical Jesus" material to find it all interesting but not faith-threatening. I think if I were to have denounced Christianity, as I toyed with some 15+ years ago, I would have done it by now, but these stories, for better and worse, have shaped me, shaped my life and since my one attempt at dumping it all failed, I figure I'm here to stay.
But I'm as prone to speculate as anyone and often these proclamations of the fictional nature of the gospels rests on more or less on major premise: Jesus is not mentioned in any non-Biblical material, anywhere. Well, there's the one mention of him in Josephus, but I've seen the argument that some zealous Christian added that to Josephus' history. I don't know. I wasn't there and I haven't researched that claim.
Reading the Bible stories about Jesus, it's easy to get the impression that he was like some rock star, getting huge crowds everywhere he went, known by everyone. Did he really attract 5000 that one time? Having grown up near a town of just under 3,000 population, I have to say I suspect some hyperbole on the part of the gospel writers. Was Jesus' triumphant entry int Jerusalem really create traffic jams and crowded sidewalks? I suspect that, too has some hyperbole. It was clearly enough to get the attention of the authorities, but how many would that take? I see protests on street corners here in Houston that attract law officers and there's maybe 100, 150 at those. And Houston has, I'm pretty sure, a much larger population that than Jerusalem did at the time. If Jesus did gather a couple of hundred folk, that would have been upsetting to the power structure.
But Jesus wasn't the only wandering preacher of the time. He wasn't the only figure to gain a following. One thing that Rome did well was that it squashed anything that looked the least bit threatening to their power structure.
So Jesus was just another bug to step on, really. He, and John before him, may have run foul of the powers that were, but it's hard to know how many like him there were. Jesus and the two thieves were not the only ones to be crucified, not by a long shot.
Thus my speculation goes like this: Only the few around him would have considered writing down stories about him. It was the growing numbers of people who shared the Jesus stories that made them famous.Otherwise, he was more or less just another obscure preacher with a penchant for pissing off powerful people.
In some ways, this obscurity, this hard-to-pin-down-historically aspect of Jesus fits the general point of the Incarnation. God became human, and not even a famous human, but this unremarkable, popular-with-the-wrong-people sort of human.
Of course that sort of obscurity---a sort of humility, really---that creates the theories that Jesus never existed as a historical figure.
(Take a moment to compare to the stories, rumors, and
controversies about someone like William Shakespeare, who lived a more
popular and public life and only 400 years ago.)
And now that I've had my say about that, I probably won't engage on the topic again.