Christmas carols

I don't understand Christmas carols. First of all, it seems to me that a lot of them don't have anything to do with Christmas (eg jingle bells, drummer boy, 12 days of Christmas)

I found a web site which describes the popular English carols:
http://www.bbc.co.uk/dna/h2g2/A832420

and another site which has the words of hundreds of carols:
http://www.hymnsandcarolsofchristmas.com/HTML/The_hymns_and_carols_.htm

There is also a Wikipedia entry for Christmas at:
http://en.wikipedia.org/wiki/Christmas

According to this, Christmas was banned in England in the 1647 but then became more popular in the 1800's:
"By the 1820s, sectarian tension had eased and British writers began to worry that Christmas was dying out. They imagined Tudor Christmas as a time of heartfelt celebration, and efforts were made to revive the holiday. The book A Christmas Carol (1843) by Charles Dickens played a major role in reinventing Christmas as a holiday emphasizing family, goodwill, and compassion (as opposed to communal celebration and hedonistic excess)."

According to Wikipedia, similar things happened in America:
"The Puritans of New England disapproved of Christmas and celebration was outlawed in Boston (1659-81). Meanwhile, Virginia and New York celebrated freely. Christmas fell out of favor in the U.S. after the American Revolution, when it was considered an "English custom"."

Maybe this explains why so many English Christmas carols seem to be written in the 1800's, because celebration of Christmas was becoming more popular in England and America at that time.

Personally, my favourite Christmas carol is "Mary's Boy Child", which was sung by Harry Belafonte:
http://my.homewithgod.com/heavenlymidis/Christmas/boychild.html