Well, yes. And while there certainly are scholars whose theological precommitments bias their views, I think on this particular question the way the issue goes has less to do with that than with the nature of evidence.
The person who, like me, is somewhat skeptical of the value of textual evidence that comes down to us has no “positive” case to make, particularly. I don’t know how the stories of Jesus originated or were propagated, how they may have changed in the telling, et cetera. Rather, my own view of it is shaped by the fact that I do NOT know those things. But not-knowing doesn’t really point to firm conclusions and exciting theses.
The mythicists have a case to put, and they are, for whatever reason, unsatisfied with just stopping at the idea that the origins of Christian tradition are unknown and somewhat obscure. It doesn’t get 'em where they wanna go. So they have to look for a “positive” case to make – one which demonstrates, in some way, the non-existence of Jesus or some specific alternative origin for the stories. I’ve read G.A. Wells and Richard Carrier, both of whom want to make the case on a kind of argument, drawing from works of textual criticism, that the earliest accounts of Jesus have him as a kind of celestial figure without an earthly life; if one accepts that, then it is susceptible to the interpretation that when later works give Jesus that earthly biography, they are layering pseudo-history onto a Jesus that originally had no historical core. I won’t go into detail here because it’s not necessary to my point – I’ll just say that my sense is that they grossly oversell what case they have to make, and I find it not absurd, but just unconvincing (and, sadly, sometimes characterized by such things as quote-mining, which, it is fair to say, do nothing for the credibility of the approach). But to the mythicist who wants to spread mythicism, some demonstration OF myth is necessary. He can’t just stand on the indefiniteness of the foundations of tradition, because that indefiniteness does not show that Jesus did not exist; at the maximum, it only suggests that Jesus not existing is a possibility to consider.
I don’t think that there is a positive case worth making on this. And so I think it’s not very surprising that scholars don’t really try to make it. I wonder sometimes how “actually confident” one might find various NT scholars on the actual existence of Jesus, if one put the question squarely. I sort of suspect that a number of them wouldn’t think it was a very interesting question – they might be more interested in the tradition than in the history, more interested in the cultural developments in the religion than in the opaque origins of the religion, that sort of thing. But if they are mostly (or near-unanimously) persuaded that the best hypothesis – whether they judge that hypothesis as near-certain or as merely likely – is that there is some historical core to the gospel stories, I suppose it’s natural that they follow lines of inquiry that flow from that. If there were a really serious and worthwhile positive case to make to say that Jesus did NOT exist, I suspect it’d get more attention; but if there is such a positive case to make, I haven’t seen it.
I suspect one could make a credible case for some sort of bias in favor of historicity, among those scholars whose faith would be made problematic by non-historicity. But I sort of think that that’s beside the point, most of the time. The reasonable person will try to evaluate the quality of the evidence offered. It does one very little good, in advocating a point, to show “bias” without more. As a lawyer in court one never says, “yes, my opponent seems to be making a pretty good argument, but look! He represents my client’s adversary! He is biased, your honor!” Rather, one has got to do the work of showing not that the other guy is biased – which everyone already knows – but that he’s wrong.
It is not, I think, that the evidence for a historical Jesus is particularly compelling – it’s that there is no alternative view of the origins of Christianity that is compelling, either. That being the case, the most “natural” inference – that there is something or other in history behind it – naturally tends to be where people land. One can doubt it; myself, I most certainly do doubt it, though on balance I’d bet for some sort of historicity over none.