Answer:
The people of the Roman Empire did not have freedom of religion. Christianity was brought to them supposedly by one of Jesus's disciples. Some people got on board with this new concept and practiced it even though there were massive consequences. It you were found to be a Christian they could whip you and feed you to the lions during to the games as entertainment. Basically anything goes. So I think the people were attracted to it because it was something they had never done before it was a new outlook and it was forbidden and everyone wants the forbidden fruit.