One of my confirmation class church history recollections (dim after so many years) is that the early Christians might have wanted to use a pagan festival as cover. If the date was approximate anyhow, it was prudent during the era of the underground church to wait until the jpagans were lining up for their roast goose and Yorkshire pudding, and blend in with the crowd.
It’s understandable how that could happen, but frankly to me that represents a Christian society that was diminishing in its boldness.
If you aren’t pushing through Christ, then you will find the world, flesh, and devil pushing you. Does not for a moment mean you aren’t destined to heaven, but your reward is then less than it could be.