Why did charles dickens wrote a christmas carol?

Your question is very interesting and at the same challenging. I researched it and it has very interesting origins: http://time.com/4597964/history-charles-dickens-christmas-carol/

In general ''A Christmas Carol'' was written for practical reasons and with nostalgia. A Christmas Carol helped Christmas to be child-centered. Dickens's novel also allows us to have a vivid mental image of snow and the horrid cold on London streets in late Dec and he associates Christmas with ghosts. Dickens's tale is highly moral in tone has a religious conception of Christmas. And while I was at it I found what were the Origins of Christmas, Halloween, and Easter. Here is the link: JW.ORG