Because it's full of obnoxious, unfunny humor; the McGuffin is forced and absurd; the conflict is also forced; Picard and crew act like self-righteous douchebags for the entire last half of the film; the villains actually have a pretty good claim on the planet, or at least just as much of one as the protagonists; the Ba'ku are unsympathetic and annoying and arrogant; and why didn't Starfleet just come out in the open and cut a deal with the Ba'ku and Son'a for use of half the planet as a heath spa or something, anyway? It's not like 300 people are going to be bothered by a Starfleet medical facility for treating people's ailments that could be located on another continent. Unless they would. Which would make them selfish jerks.
No. It's a movie that's powered by everyone being selfish asses, and I'll be perfectly happy if I never see it again.