Mostly because there’s a new modern storyline to parallel the historical one. And a random Hugh Jackman badly singing Mandarin. (I can get people not liking that. It was random and awkward.)
But platonic life partners? Lady composer? Maybe the fact that movies are ‘less intellectual’ and it was decided that viewers who didn’t read the book needed a modern parallel in order to empathise with the characters? (And there were people complaining it was too hard to distinguish the two time periods. Really?)
So I liked it. Though fair warning given for sad endings, people dying, historical sexism and domestic abuse, and those warnings should tell you it is not the happiest of movies.