When someone says “there are resources in space” it’s more accurate to say “all of the resources are in space”. When you use propellant, you’re not just moving your rocket, but the propellant you’ll be using later. Building a huge launch vehicle to leave Earth, mine an asteroid, and return is a terrible way to get resources back to Earth. But manufacturing requires infrastructure, which means that a lot of what you recover in mining will be used to support the in-situ infrastructure that supports the mining. Asteroid mining isn’t about someone somewhere making trillions of dollars, although that will probably happen.