Completely agree, it’s difficult to understand exactly why all the righteous blood is charged to apostate Israel but that’s what it says.
Let's look at the text again.
Matthew 23:34 Wherefore, behold, I send unto you prophets, and wise men, and scribes: and some of them ye shall kill and crucify; and some of them shall ye scourge in your synagogues, and persecute them from city to city:
35 That upon you may come all the righteous blood shed upon the earth, from the blood of righteous Abel unto the blood of Zacharias son of Barachias, whom ye slew between the temple and the altar.
36 Verily I say unto you, All these things shall come upon this generation.
What I see these being accountable for are all the righteous blood shed upon the earth, from the blood of righteous Abel unto the blood of Zacharias son of Barachias, and those of them they shall kill and crucify; and those of them they shall scourge in their synagogues, and persecute them from city to city.
None of that takes into account any righteous blood shed upon the earth post 70 AD though, assuming 70 AD was the fulfillment of this in verse 35---That upon you may come.
Obviously, there is still righteous blood being shed upon the earth post 70 AD, and if these were already judged, so to speak, in 70 AD, we can't stop there and then insist end of story, nothing else to see here. And surely events recorded in Revelation don't end with the destruction of Jerusalem in 70 AD either, assuming some of it even involves 70 AD, where I myself disagree that it does, then disregards the rest of human history post 70 AD to that of the 2nd coming, as if it is unimportant, but instead skips straight to the end, meaning Revelation 20:10-15.
IOW, something like this---Revelation records events involving the first century up until 70 AD, then is silent on human history post that time, then ends with what is recorded in Revelation 20:10-15. Yet, this is already proven wrong via Revelation 12 alone.
Clearly, though maybe not to everyone, that chapter spans events pertaining to the birth of Christ through that of the time of the beast in the final days of this age, meaning this in Revelation 12:17---and went to make war with the remnant of her seed, which keep the commandments of God, and have the testimony of Jesus Christ. Maybe it can be argued that this already began 2000 years ago, and maybe that is even true, but even so, the fact saints are still being persecuted, and some even martyred, today in some parts of this world, this still further proves, like I already indicated, that ch 12 alone spans at least 2000 years, maybe more, depending on when Christ actually returns.
Unless one wants to argue something preposterous, that no saints have been persecuted after 70 AD, that no righteous blood has been shed on the earth post 70 AD .