So according to my understanding the Roman religion and many other pagan faiths of their empire often didn't demand exclusive worship of their gods and neither did many of Christianity's rivals like Mithraism. Obviously Christianity seems to be more likely to demand exclusivity but is it know if early churches ever took a liberal interpretation of lines like you shall have no other gods before me as meaning you had to consider Yhwh their main god but could still keep their original pantheon on the side? Given that the church made other pragmatic moves like dropping a lot of the old laws concerning things like circumcision that the Romans didn't approve of I wondered if they might have ever made a move like this to try to be more attractive to non-Jews.
Only heretics would have done so. If you read in Saint Paul's letters especially to those in Ephesus (Timothy and Ephesians), where they had kept the whole having sex with prostitutes to "worship." There may have been similar things throughout history, but there's never been an official movement to include pagan holidays or practices, Christianity in was pretty insistent on NOT being anything like paganism, even to the point of death.
It appealed to many people because of its radical acceptance of everyone. In christianity, all were equal. It put women in direct conflict with their husbands, brothers, and fathers because of its value on women. Saints Mary Magdalene, Thecla, Nina and many others bear the title "equal to the apostle" (Mary Magdalene is the Apostle to the Apostles). Saint Lydia funded Paul's missionary work, Saint Priscilla is held in higher esteem than her husband.
It also preached to treat slaves well and to equalize relations of the poor and rich. That's how it grew so much. Read some of the writings of Saint John Chrysostom and Saint Basil the Great, their writings on the rich and poor are astounding.
So it wasn't the adoption of pagan practices that made people want to convert, but a religion that was unlike any other and treated all people well