2) It’s hard to get your head around the relative velocities you can get from orbital debris. A bullet travels at around 750 miles per hour. A satellite in low-earth orbit travels at 17,500 miles per hour. Orbital debris could impact a spacecraft at something like a cosine loss of that number, which depending on the exact inclination could be on the order of 10,000 miles per hour. So a factor of 15 faster than a bullet.

Shielding takes mass. Mass is expensive. It costs $5000/pound to launch mass into low earth orbit;