While it’s true that there are a lot of Christmas decorations in Japan this time of year, most of it lacks any religious connection (no Nativity scenes that I can remember) and that left it feeling a little hollow and soulless for me when I lived there. On the other hand, Colonel Sanders at KFC does look pretty good decked out for Christmas.
It's probably a commercial celebration.
Look on the box of Christmas decorations you purchased lately--it reads "Made in China." In the fifties and sixties, the box would have read "Made in Japan."
I don't think it's bad. Christmas was originally a pagan holiday, corresponding to winter's shortest day (forget what it's called.) It also had a psychological component, light in darkness, gorging in anticipation of the long winter, evergreen trees to recall spring. It was also associated with the Persian cult of Mithras, celebrated on December 25. There were many converts in Rome, especially in the legions.
I think the Catholic church adopted the day and assigned a Christian character. Protestants, especially the Puritans did not approve. Was it Cromwell or the New England Puritans who outlawed it.
The essential Christian celebration is Easter, though that has pagan precursors as well.