Because when humanity finally establishes itself outside of Earth's gravity well in a self-sufficient fashion, the game is up for every little tyrant and leech on the planet.
Unfortunately, it is pretty clear at this point that those humans aren't going to be Americans. We sold that birthright for a bowl of socialist porridge.
That is exactly right.
Those in power now learned their lesson, colonies are only colonies until they become self sufficient, then they are a force. You simply cannot govern people at a distance unless they allow you to govern them.
Releasing humans into the solar system would be a technological boom.
Those in charge now would rather reduce humans to a manageable population, than find a way to send "excess" population to the stars.
It is always about control and power.
“We sold that birthright for a bowl of socialist porridge.”
And a “free” set of false teeth.