You might be mistaken actually. The Mawlid was celebrated for centuries in most Muslim lands and many scholars have permitted it. It was never really frowned upon.Islam generally frowns upon celebrations of prophets birthdays. The Mawlid was historically frowned upon.
Furthermore, I did ask some sheikhs this and the answer was three fold.
1. Islam actually believes Jesus was born in January, in accordance with the Orthodox.
2. Christmas is a pagan holiday and we know what Islam thinks of Paganism.
3. Islam frowns upon copying non-Muslim traditions.