Here is one argument: The books of the bible were written 50-100 years after the alleged life of Christ. No original Greek manuscripts have been found, only translations from as early as 125 AD. Actually, it is likely true that they weren't translations at all, that before this point there was no bible just limited writings and lots of oral reiteration. You can see how many are skeptical of the authenticity of the claims of miracles when considering this history. Then there is how Christianity came to power within a century around 300AD. Some argue it was because Christians aggressively tried to appeal to pagans. They also argue that during that century the new emperor and Roman authorities saw value in the Christian Church's appeal to the people (pagans and Jews) and its ability to collect capital. There is also something to be said about the submission to authority that Christianity taught, but that was essential to any authority adopting any religion, so while it was essential that Christianity taught submission to authority it was not exclusive to it.