I love Christmas Carol and have a facsimile first edition which I read every year, so I can recite passages of it. There was a time, when my first child was little, that I could recite the Grinch by heart, too, because I read it to him so often. However, although I love the Grinch, Christmas Carol is by far the more important story of the two for me.
It is true that Christmas wasn't a big celebration in English-speaking lands in the 18th century, and interest in it was reviving during the 1830s & '40s (Christmas Carol came out in 1843, if memory serves). I believe the English stopped celebrating it in a big way during the Civil War period (1640s), when the Puritans were in control for about twenty years and outlawed it (too Catholic & too pagan for them). After the Restoration, I think people were afraid to have much to do with religion, actually, since they had had a civil war about it. So Christmas was kind of anemically celebrated compared to what it had been during the Middle Ages and Renaissance. I think it is true that businesses and governments, etc., didn't routinely take off for it. That started to change when the English began taking an antiquarian interest in their own traditions and past, and when the German diaspora of the 19th century caused them to spread their customs (Christmas trees, for example) around the world.
Many of Scrooge's comments early in the novella are expressions of philosophies in vogue during Dickens' lifetime. So, yeah, you do have to put it in period context to understand where Scrooge is coming from. But I also agree that you get lots of clues within the story that Scrooge didn't have to be the man he turned out to be. He was a sensitive, imaginative child who had been raised in a mostly loveless environment, and he did fear poverty tremendously because of his early experience. I don't necessarily think Belle's rejection is altogether what "turned" him, since she rejects him only after it becomes apparent to her that he is growing so avaricious. But without her ameliorating influence, there is no check on his self-centered nature, which is certainly driven by fear.
Scrooge is a very complex, interesting character. My favorite interpretation of him on screen is George C. Scott's (1984). I think Scott gets Scrooge's sarcastic humor and intelligence just right.