Also, most contrary documents (and people) were burned. Many of the most important source documents discovered in the last century only survived because they had been deliberately hidden from the church's PC police. Christianity used to take the same line on apostasy and heresy as ISIS.
c.f. "Everybody in 70's China was a Maoist because the only surviving documents from that period are Maoist."
There's a really interesting discussion of the evolution of Christian doctrine in (I think) Karen Armstrong's
The History of God. She documents how what we are taught as Christine doctrine now was only one of many wildly divergent strains of early Christianity, and in some doctrinal cases not even the majority position. Basics like the Trinity or the cross as the symbol of faith or transubstantiation would have struck early Christians as bizarre lunacy.
This was a very messy, very worldly history of power struggles between the
various power centers (Rome vs Alexandria vs Antioch etc). When one strain finally got enough secular power to extinguish the others, culminating with the First Council of Nicaea in 325, there was a ruthless effort to obliterate all record of all the others. But in reality Christianity in the early period was extremely volatile and the creed didn't settle down until somebody finally had the firepower behind him to kill off all the competition.
tl; dr: Not only was Jesus not a Christian, the vast majority of early Christians weren't what we call "Christian."