The better question here is why does one that thinks he did not exist care?
The basic fact of the matter is that one of faith is going to believe that Jesus existed. The very basis of faith is that proof is not necessary nor even sought - it is personal and the 'proof' for faith internal. For those that do not believe, does Jesus' existence change anything? Not at all. Christianity is still here, it's effects and influence still here and ultimately trying to state Jesus did not exist is an exercise in futility. You are not going to convince anyone that has faith and those that do not have faith are not really in a position to care one way or another.
The only reason that I can see for trying to bring something like this up and defending it (Jesus not existing) would be to throw discredit onto a religion which is, at the very best, nonsensical.
Your post is like proverbial March weather: In like a lion, out like a lamb. First, you ask a legitimate question, but then pollute it with your own anti-religious biases:
The "basic fact of the matter" regarding Jesus' existence is historical evidence, not merely belief or "faith internal." Whether or not you believe Christianity to be "nonsensical" is neither relevant nor particularly interesting.