Every one of the songs you used was *very* popular. I’m only referring to the way Billboard normalizes radio play with sales. Back in the days before Apple, Pop music got LESS radio play in December, since many stations switch to Christmas-dominated formats temporarily, but almost half of sales came in the Christmas season. Their weekly top 100 was a balance of airplay and sales.
But the way they normalize for Christmas sales made January light-pop have an advantage. By the late 1980s, light-pop songs peaking in January held the top spot on the annual charts almost every year: Careless Whisper (1985), That’s What Friends Are For (1986), Walk Like An Egyptian (1987), Faith (1988). My Prerogative was #2 for the year in 1989, despite being #1 for a single week in January.
Eventually, Billboard seems to have recognized the urgency of the problem, and started keeping better track of when singles were actually sold, so middle-aged people replacing their Bon Jovi albums with “Careless Whisper” weren’t counted.
Interesting, because I never heard Christmas songs played on any top 40 station until this past decade (if that; often it is general-pop which includes long-old things). I’d say that is post-Apple. Maybe to compete with XM and the like.