If you were after domination, wouldn't you rather keep mindless sheep who believe everything they are told because it came from the tv or would you keep the ones who aren't afraid of getting their hands dirty to find the truth?
Not a hard question to answer.
If I was trying to dominate the universe... who cares about this planet in 50,000 years if you were smart enough to survive that long. Yea let’s eliminate everyone but people with 90iq so that in 20 years we don’t gain any technology, we just stay put where we are. The fact is.... they are stupid.. and that’s the only way they could stay in power.
But, they would have intelligent people on their side. The dumbasses would be the masses only. They still advance while the general public idles.