The Harry Potter universe was unique because, through Harry, audiences and readers were introduced to a Wizarding World that had existed before him and would continue even after. As a result, many traditions and customs were foreign to Harry, but fans learned about them through him. This included getting an invitation to Hogwarts, choosing a wand, and, of course, being sorted into the proper house.
The Sorting Hat was an artifact that had been around even before Hogwarts, with legend believing the hat belonged to Godric Gryffindor. It was proposed by Godric that, after the four founders had died, they'd need a way to sort students into their houses. As a result, the Sorting Hat was born. In the movies, it was believed that the hat was a stern and sometimes intimidating judge of character but always just in its rulings. But as the books proved, it also had a heartwarming tradition that the movies excluded -- singing.
How Long Has Hogwarts' Sorting Hat Sang?
Each year, the Sorting Hat sang a new song for students, mainly to introduce itself to first years and to establish its purpose in sorting students. But each year, possibly through Dumbledore and heavy thought, the song would change. Even Ron was under the impression it took the hat at least a year to orchestrate a new tune. However, certain events would dictate that this may not always be the case, such as in 1995, when the hat delivered an ominous warning.
1995 was the first year when Harry and his allies had to confront Lord Voldemort and his allies but were still unprepared for what they would face. Even still, the Sorting Hat still did its best to warn the students in that year's song with the verse, "Oh, know the perils, read the signs, The warning history shows, For our Hogwarts, is in danger From external, deadly foes." It's still unclear how the hat knew that Hogwarts was in peril specifically, but it showed that it both paid attention and used its own experiences to create songs that informed and encouraged serious contemplation.
Singing Changes the Sorting Hat in a Big Way
When Harry Potter sat down to learn what house he would be sorted into, he was intimidated by the surly look of the hat and its admittedly intimidating tone. It spoke to itself but managed to speak the truth about the character of each student and made it completely justified to be unsettled by it. However, the movies excluding its song played a big role in why it seemed so intimidating to so many. Had the song remained, fans who have yet to read the book would see a hat that's more old and wise, with a knack for wittiness.
Singing would've also brought a heartwarming quality to the hat that was necessary for Harry's later years at the school when the darkness was starting to spread. First and foremost, Hogwarts and the Sorting Hat were created to make students comfortable with their new environment, and singing was a great way to put them at ease. As a result, while not shown in live-action, singing was still one of the Sorting Hat's best traits and Hogwarts' most entertaining tradition.