It's strange to me. It is like your view of this adventure is so narrow, that you can't imagine someone else playing it differently than how you describe. I am sure, if someone said, "Hey, we were running Rime of the Frostmaiden, but then the players decided they wanted to help destroy Ten Towns because one of the towns was sacrificing people," you wouldn't have a problem with it. They did what their table decided to do. The DM may have presented a different context.
So why is it so hard to believe that some people played this adventure and didn't just slaughter everything? Why is it so hard to believe that for many tables, they formed factions with one of the groups? Why is it so hard to believe the DM didn't set up one of the groups as really, really, really, evil? (Maybe the intro was that group killing a man and terrorizing his wife.) Why is it so hard to believe that certain DMs set part of the caves up as an evil cult, that if left alone, would eventually kill all the creatures in there - and then the Keep?
It just seems myopic.