Why? Josephus refers to about 35 different Jesus'. Jesus was a common name. The confusion lies with gMark, some scholars have suggested that Mark combined two very different religions into one when he wrote his gospel story, he combined a Galilean Jesus movement with a Jerusalem Christ cult. Any historical Jesus may stem from the Jesus movement but Paul's Christ has no basis in history that anyone can be sure of.
Then the question is rather, how many historical Jesus-es were there, not if there was none at all.
Is it really possible that the Galilean Jesus movement just invented a magical and invisible Jesus they all managed to believe in, without anyone leading them or doing the inventing? They all just had the same ideas about a "Jesus"? And at the same time, a cult in Jerusalem also springs up the same way. No one knows how or why, but all have an idea of the invisible Jesus that says new and different things about belief and God. Is that really possible? No religion has done that. If that's how it started, then that is a greater supernatural miracle than a supposed resurrection. (FYI, I don't believe in a physical resurrection, just so you know, we're on the same side there.)
What I'm saying is that if Josephus talked about several physical and historical Jesus-es, and all, or few, or one of them were the seed for beginning of the religion, then that's the "historical Jesus" or "Jesus-es" that we're looking for.