Because when comparing apples and oranges we have to first identify what is what. What is Christianity? My Christianity comes from Clement of Alexandria. That's whom I think is "Christianity" for me. And what do I see? Chronology.Why do you insist upon such strict parallels?
When I look at the gospel there's a chronology. Whether it is the Marcionite gospel or the Catholic gospel. It's not just a "novel." There is an overarching "chronology" where Jesus's appearance fits. The chronology isn't superfluous. It's essential. As such it's not like all that you're citing here.
Christianity assumes that it's 6000 years from the Creation of the world. As such it can't be "myth." It isn't being proposed to exist in some "never never land." It's 6000 years. Times up. Here comes God.
Christianity assumes that Daniel's 490 years has been fulfilled with Jesus. How can it be "mythical"? Why would the gospel cite Daniel's seventy weeks in a myth that could happen at any time with someone who never existed as the fulfillment of Daniel's prophesy?
Christianity assumes that "he was crucified under Pilate." How can that be reflective of a religion that was "made up." Why bring forward Pilate, a real person if the narrative was just a "novel." Why emphasize the "under Pilate-ness" if everyone was "really" think this was a myth.
It seems to me that these discussions have a conspiracy mind set about them. A nefarious inner circle of evil men made up a lie. Whether the Pentateuch or the gospel. Why so? Because the people promulgating the conspiracy don't like the Bible.
So this is my push back.
At the same time I see the earliest traditions see Jesus as a god who in some sense came into the world by extraordinary even supernatural circumstances. I see these are the twin poles of deciding whether or not Christianity was "historical" (which I think it was in some sense). I don't think an appeal to Buddhism is particularly relevant or helpful except for distracting us from keeping our eyes on what Christianity is.