I don't know. It's not like they ever had to deal with that with their private jets, huge mansions etc. They're living a pretty comfy life. I think they want to rule over humanity, but a different, more obedient kind. Unable to genetically engineer all the masses of people, they might just want to reduce the pop so they can realistically implement their transhumanist endeavors. I don't believe for a second that they actually give a shit about the planet, they'd rather suck it dry and then find another suitable planet.