Somehow the conspiracy of the early church was SO good it kept a cacophony of almost-Mark, Luke, Matthew, and John gospels from surviving for posterity in spite of a smorgasbord of religious practices and beliefs in the region. There are small variations of wording in gospels and disputes over placement and presence passages, but they don't show the weird kind of thinking that appeared in the post-year-100 pseudo gospels that have psychedelic things like crosses floating out of tombs. The four recognized gospels and known variants are very focused on Jesus and very realistic in tone.
Umm.. Did the possibility occur to you that the Synoptic Gospels resemble one another because they mostly copied one another (which the Church acknowledges) and that the reason they were made canonical is because they resembled one another?
Hmm.. I shouldn't have said the Church acknowledges the shared text; I'm uncertain whether that's true (and almost certainly not for all denominations). I should've said New Testament scholars acknowledge it.
BTW, in case you haven't noticed, there is at present a cacophony of texts and a smorgasbord of practices and beliefs within Christianity. The reason they don't strike you that way is probably merely because you're accustomed to them.
Conspiracy? No, that wouldn't be the word that I'd use. Rivals in competition? Yes.
Each community had their rites and oral traditions that they'd claim from a Apostle or someone who knew the Apostle (the patriarch). Many of those communities were originally of the "Eastern mysteries" style pagans. These claimed special knowledge of god(s) and secret rites that were forbidden to outsiders. As the apostles spread the story of Jesus, these sects would replace their deities with Jesus in worship but retained the idea that they had special, and therefore superior, knowledge of God.
The bulk of Christendom at the time, churches of Peter, Andrew, and Paul shared the same creed and teachings and cooperated as one church. Particularly in being firmly opposed to these Gnostic sects as being in error concerning the faith. But since there was no hierarchy of authority among the churches, they could only warn or try to persuade the others (1 Tim 6:21, St. Justin's "Syntagma", and St. Irenaeus).
Each community would combine or reject doctrine and traditions from the other sects as they wished. Sometimes by adopting a "foreign" tradition they might have to correct or embellish their established doctrine.
About 100 years after the Crucifixion we see individual sects following distinct "schools" of thought: the communities of Valentinus, Basilides, Marcion, Polycarp, Thomas, and John were some of the major groupings.
As the church grew, the factions competed with each other as to who had the "correct" doctrinal faith. By the time Constantine recognized the church in 313 and the Council of Nicaea, the game was pretty much over. The Peter-Paul-Andrew juggernaut, joined by a splinter sect of the Johannines (and their Gospel of John) became the dominant creed.
If you don't have it book marked, let me recommend Early Christian Writings
Sections (in no particular order):
'Signs Gospel',
'Book of Hebrews',
'Gospel of Thomas',
'Gospel of Peter',
'Gospel of the Ebionites',
'Acts of Pilate', and
'Pistis Sophia'