They changed a lot of things in all three of the LOTR movies. One example: Arwen was not such an active character in the books, but emerged as such in the first movie—in the book, it was an elf called Glorfindel that met Strider and the Hobbits when the Nazgûl were pursuing them en route to Rivendell, and it was Elrond and Gandalf that “commanded” the flood at the ford of the river Bruinen that washed the Nazgûl and their horses downstream, not Arwen.
(The cartoon directed by Ralph Bakshi replaced Glorfindel with Legolas, BTW.)
Digging in the weeds there. Give an old man a break, I read the books in 1976! lol
Some of the changes maybe didn’t need to be done... But I understand why they were done. There’s Sooo many characters in LOTR. Lots of strong roles in the book that would frankly be confusing in the movie. The pace of a movie has to be faster, and introducing too many one-appearance characters makes a movie choppy and hard to follow. The movie already had several strong male and female roles to develop and just didn’t need any more.
One of the more glaring changes/additions, to me anyway, was the appearance of the Elves at the Battle of Helm’s Deep.
That and the elimination of the Ents’ contribution to the end of the battle.