Recreate his wife

This is likely a true theory, and a lot of signs point to it being correct.

Once Curtis' beloved wife died in childbirth, he has never been the same. He has to deal with the grief, and has to deal with the frustration of his curious child who would ask about her mother. The child is also very similar to her mother, which can bring painful memories as he is reminded of his wife every day.

He tries to bring back his wife by using genetics and DNA sampling. He has locks of her hair, which is most likely the main DNA sample that he would use. He also held on to all her stuff in the attic, although those are more likely keepsakes.

When his experiments fail, he gets more and more frustrated, taking out his anger on his daughter. He tries over and over, only to create monstrosities. His failures live on to remind him that he has failed, which is why he decides to leave. He realizes he cannot bring his wife back, and that the more he tries, the more anger he will put on to his daughter. He does not want to hurt Daisy, and so he decides it is just best to get away.