The leader of the Loners and the Heartless Woman are both shown to share a defining trait and were meant to be together.
In this future setting, turning people into animals is still technologically impossible.
When David and the maid take the Heartless Woman into the transformation room, David's narration says that he'll never speak about what they found in there, but it was horrifying. This could be that they found out that the transformation room was actually an execution room
They don't turn people into animals. What we hear about the technology suggests it involves transferring the brain and the eyes, which clearly makes no sense because implanting a human brain into a lobster is impossible in terms of space requirements if nothing else. No, people who fail to find a partner are simply killed; their family are then presented with an animal and told that this is the "transformed" subject, a fiction intended to make the system more palatable.
They're trying to replicate human civilization and emotions are a really bad at it. Turning into an animal means getting your programming transferred to an animal robot. The organs mentioned getting donated are just robots parts.
- This is honestly the only way the movie makes any sense. Why do people need to be in relationships so bad? Well, because that's what humans did, therefore robot humans must as well.
"The animal no one wants to be" is a rabbit
Given the huge volume of rabbits that are seen in the woods, and promptly captured, killed, and eaten, perhaps becoming a rabbit is the worst punishment the Hotel thinks they can bestow.
The Leader of the Loners was in love with the Nearsighted Woman.
When David began his affair with the Nearsighted Woman, the Leader blinded her so the two of them would no longer share a trait and couldn't be together anymore. After that, she let the two of them do as they please, which seems like a pretty light punishment compared to what we saw others go through when they were caught having affairs. Keep in mind, David and the Nearsighted Woman had a secret code they used to communicate with each other via hand gestures. In a similar manner, the Leader and the Nearsighted Woman spoke French to each other and seemed to be the only two who knew the language. In essence, both the Leader and David had their own ways to communicate with her. While French is a language anyone can learn, the Woman's relationship with David was that much more special as it only existed between the two of them. The Leader was jealous but didn't inflict the usual punishment against the Woman since she still loved her. Instead, she opted to find a way to destroy their relationship.