It's because billionaires are planning on living forever.
When you are going to live forever you won't be able to keep it a secret.
Controlling 10 billion people is much different than trying to control 30 billion.
When illness and death is no longer a concern for you, your only concern will be dying at the hands of another person.
Forever is a long time.
They want the whole planet.
The Great Unwashed use up valuable resources. In order to ensure a long and comfortable lifestyle, the elites need to eliminate the poor.