Many of the Christmas carols that were prohibited, and early Christmas carols in general, had lyrics that conveyed joyous and merry themes instead of the serious somber words present in church hymns. Around the time when carols were banned, some composers and musicians composed non-religious songs that had extremely varied choral music, which they called carols, for Christmas. After Christmas carols again became popular, a lot of those songs were re-arranged with fresh Christian lyrics and utilized by the church. Making alterations to Christmas carols continues in a different way today with pop artistes singing the carols to different tunes and melodies to give them a style that characterizes the particular artiste. Having Christmas carols with tunes of modern-day or popular music of today means that they're also more likely to endure because younger listeners will be interested in listening to any music that is done by their favorite or other popular singers.
Read more: The History of Christmas Carols