There are two Christmas's in this day and age.
Christmas=The day Jesus was born.
and
Christmas=The day Santa brings good boys and girls presents.
Sure the first was celebrated first, but it's not as popular as the gift giving season.
Christmas- the day all the big companies get together and force people to buy things in the name of religion. It's simple to say that 'modern' christmas started like that. now, Christmas has become almost a secular holiday. why? so the marketers have a larger target market. it's as simple as that