In fairness, there’s a lot more to pull from compared to Thanksgiving, and few holidays really measure up to the hype and splendor of Christmas. In either case, one can definitely dispute the validity of Life Day being tied to Christmas if we’re just talking about the holiday special, but not when pulling in all the other references.
There’s a case to be made in regards to the special if Life Day was originally conceived with Christmas in mind, but there’s no disputing the expanded Star Wars universe has certainly transformed it into a Christmas-equivalent holiday.