Let's do the math.
• a single asteroid can contain up to $20 trillion worth of metals
• it could cost $27 Billion to mine an asteroid
With that in mind, why
don't we already have asteroid mining? Why haven't we had it since the cold war space race?
The answer, because a self-sustaining space colony would be the corporatocracy's worst nightmare.
Barring some soft scifi-tier breakthroughs in engine technology, it'd always be cheaper to manufacture necessities on site from local raw materials than ship them from earth. So the corporatocracy wouldn't be able to maintain control through the threat of boycotts of essential products and raw materials. Likewise, importing scabs to decrease the value of the colonists' labor would be obscenely expensive and lightspeed lag would mean telepresence wouldn't be practical. Furthermore, the corporatocracy couldn't give a rebellious colony the gaddafi treatment, since the same spacecraft engine technologies which would be necessary to travel to the location of and establish a space colony in the first place could be very easily repurposed into
ensuring MAD.
We've had viable technological concepts for colonizing and exploiting the resources of the solar system since the cold war space race and the potential profits are absolutely immense, so why are we only seeing the Musks and Bezoss of the world throwing funding at private spaceflight
now rather than as soon as it became possible? Because the technology to get there and acquire useful resources was one thing, but the computing technology to do so with entirely robotic labor rather than with human astronauts who could inconveniently declare independence as soon as their colonies became self-sustaining and possessors of MAD deterrence with earthbound civilization's monopoly of force was another.