I think they are creating a hybrid race with our genetics to eventually repopulate the earth because they consider the human race a failed experiment so they are going to try to redo it again. I think they have been doing this for thousands of years, manipulating the population of earth with things like the great flood with noah’s ark, the black death plague, massive volcano eruptions, the spanish flu. I think they are finalizing & making the last little tweaks and modifications to their new race before they purge the earth again and restart the experiment until they finally create a perfect species that can use technology harmoniously to evolve into a more advanced race who explore space and the universe and do not compete with each other, kill each other, pollute the environment, or put money above everything else, etc.

The goal of their experiment is to figure out the instructions for creating an advanced species similar to themselves who live in harmony because they consider this successful. Then the master race aliens can fly around on their saucers going from planet to planet creating advanced harmonious life forms there, while monitoring their progress of course. It would also make sense if their species was dying so they need to create a new one, kill 2 birds with 1 stone.