Because the Mythicism debate is important to have.

Scenario 1: there was a street preacher illiterate magician who operated for about six months and one day got an idea to attack Rome and Rome didn't care for that. The result was the world's first and second biggest religion.

Scenario 2: Paul took the James con and spent about 40 years working on it. Improving it. Make sure it brought in the crowds. The result was very interesting stories that involved the whole family in an experience and it was that that ended up taking over the world.

Frankly the first scenario is pretty scary. That crazy guy with the cardboard sign saying the end is near? All it takes is him to get shot by the cops and civilization will be in ruins 300 years later. I am much more inclined to believe that the entire practice of baptism, communion, singing together, waiting for Holy Spirit to speak through you, demon casting out and the plot skeleton of Mark came from a determined guy who ruthlessly not only stole from the best but was willing to be a workaholic with his material.

So yeah it does matter. All humans on earth are shaped by these events. If we are such that a person with no original ideas can still win we are in a lot more danger than if we lost to a person who had a new idea every Sunday.

Even if the biblical Jesus was a real guy who said literally everything ascribed to him he would have still been hundreds of years behind the thinking of the Empire.