This is what ChatGPT thinks some possible reasons are:

Genetic Research: Aliens might seek to understand human biology or enhance their own genetic traits by integrating human DNA.

Survival of the Species: If the aliens face extinction or a dwindling population, hybridization could be a way to ensure their genetic legacy continues.

Cultural Exchange: Hybridization could serve as a means to foster better interspecies understanding and cooperation, blending cultures and perspectives.

Adapting to Earth: Aliens may need to adapt to Earth's environment and human physiology could offer advantages in survival and integration.

Technological Advancement: By combining human ingenuity with alien technology, both species could achieve advancements that neither could attain alone.

Exploration of Consciousness: Hybridization might be pursued to explore the nature of consciousness and intelligence, creating beings with enhanced cognitive abilities.

Social Experimentation: Aliens could be conducting a long-term experiment to study the social dynamics of a hybrid society and the implications of interspecies relationships.

Ethical and Moral Inquiry: The program could serve as a way to explore ethical questions around identity, rights, and the definition of being.

Medical Benefits: Combining alien technology with human biology could lead to breakthroughs in medicine, potentially curing diseases or enhancing physical abilities.

Preparation for Future Threats: If there are cosmic threats (like asteroids or hostile species), hybrids might be better suited to face those challenges.