> Precious industrial metals and beamed solar power would be one thing.

I think you're dramatically underestimating the distances involved to the asteroid belt.

Beaming power over one to two astronomical units is something in between impractical and a death-ray superlaser. (And that's assuming Earth is exporting the energy, because the other way around makes even less sense--the asteroid belt only gets 10 to 20% as much light.)

> bananas

Lastly, sterile environments on Earth will be wayyy easier and cheaper an equivalent facilities in orbit, to construct, maintain, and house a workforce, etc.

The problem of screening/cleaning everything that passes through the airlock is the same regardless of gravity.