If the Tacitus passage on Nero, the Great Fire, and Christians is an interpolation, why?

I addressed week before last week how John Drinkwater handles the infamous passages from Tacitus' Annals about Nero's ALLEGED cruel punishment of Christians after the Great Fire. Beyond what I already knew about the Great Fire, about Tacitus in general, and about the Greek itacism and other problems with the specific issues in the passage, I also relied on this piece from a religion Wiki (warning: friendly to Jesus mythicism) which gave me more food for thought.

Tertullian and other Church fathers cite no such passage, and it appears not to be referenced by any Christian before 400 CE.  Sulpicius Severus, ca 400 CE, appears to be the first Christian to write about it, but his account in his "Sacred History" is hugely suspect. It's basically a "blown-out" version of Tacitus. It also gets many other things wrong, starting with claiming there was a massive number of Christians at that time, then that Nero outlawed Christianity along with starting the persecutions. Clement I, especially if one goes by "traditional" date and provenance, would have readers who would have remembered this, had it happened. He doesn't mention it. Celsus surely would have flung this issue at Origin, had he known of it, and of course Origen would have found some way to try refute it. He doesn't discuss it. Tertullian, who cites Tacitus a fair amount, doesn't mention it. Nor Eusebius, the first Christian historian.

And, some early writings actually explicitly counter Tacitus' claim. Brent Shaw, in an academic journal, extracted and summarized here by Charles Mercier, has the details on the possibility this is an interpolation. (Mercier then has a Part 2, which frames Catholic touting of Neronian martyrs within Reformation hagiography.) Shaw, per Mercier's Part 1, doesn't totally agree with the Religion Wiki take on why this is possibly an interpolation. As noted, if the passage IS genuine, the best and most we can derive from it, in my opinion, is that Tacitus was doing a bank shot to smear Nero by saying his torturous deaths were so cruel that Christians got sympathy. (I'm not fully ready to commit to it being an interpolation, as that's an argument from silence, and to do otherwise risks petard-hoisting. That said, [motivated reasoning alert?] the idea that there are degrees of silence would nuance that.)

But, what if it IS an interpolation? Why?

Let's say that Christians of 300 CE or later read Suetonius, and took his account that Claudius expelled the Jews who were engaged in Messianic disturbances (sic on my interpretation of ChrEEStos) and instead took that to be Jesus. 

So, why extrapolate from there to Nero?

Per my big piece about the differences between "antichrist," "man of lawlessness" and "666/The Beast," and John Chyrsostom chiding Christians of his time for visiting synagogues? At 400 CE, Christians still would have known enough Hebrew and/or Aramaic to know that the "666" was Nero. (As I note there, "Nero Caesar" in the Hebrew alphabet is נרון קסר‎ NRON QSR, which when used as numbers represent 50 200 6 50 100 60 200, which add to 666. See the link at the top of the paragraph for more detail.) They would not have know that this could have come from a disciple of John the Baptist who wrote the non-Christian core of Revelation, so they asked, "WHY is Nero the Beast"? And, they created the answer. There may also be angles related to Constantinople as the New Rome and other things.

That said, that leads to a third theoretical option besides Tacitus being true here. That is that there were messianic disturbances at this time, tied to the precursor of the revolt and the First Jewish War in Judea. We have Claudius' previous expulsion of the Jews from Rome. Tom Holland, in his book "Dynasty," notes that, according to Valerius Maximus, the first Roman expulsion of Jews happened way back in 139 BCE. That would have been just after the establishment of the Hasmonean kingdom. And, while the Christian population of Rome at this time (setting aside the issue of them counting themselves separate from Jews or not) was only 1/10 of 1 percent, Jews made up around 5 percent of Rome's population, as the past expulsions had in general not been permanent and Jew/non-Jew and Jewish/non-Jewish, to get at both culture and religion, differences weren't as sharply noticed as in Christian Europe, making returns easier.

But, how likely is that? Suetonius had mentioned the expulsion of the Jews under Claudius; surely he would have mentioned this, too, one would think. Tacitus and Suetonius would have used more explicitly anti-Jewish language, as both were writing after the First Jewish War. And, after the "separation" started, Christians would have cited this among anti-Jewish polemics.

Of the three, an interpolation seems more likely. The double bankshot seems less likely. The Jewish Messianic revolt seems not much more likely than Tacitus telling the truth here.