I assume it is a relevant enough concept to flying an aircraft (which also happens to be the context of TFA) that you learn about it while flying.

I guess another thing worth noting is that "glide ratio" isn't the same as "gliding" in the "flying a glider" context.

The space shuttle is probably the most famous glider, and was described as "a flying brick" and getting it to the ground at the right spot was very much a matter of glide ratio. Worth noting the space shuttle's speeds started off as hypersonic.

By comparison, a typical glider's built to be able to take advantage of air currents to regain altitude, and I'm not sure how weight affects that.

Make a paper airplane and drop it. It likely won't go much further than your feet. Throw it gently and it will go some distance. Throw it harder and it will go further. Glide ratio is the horizontal distance over vertical distance. The vertical distance is the product of (lift - mass)*t^2 where lift is a function of the shape of the wings and the airspeed. So given a higher mass and the same lift, the time to hit the ground will be less when the glider is dropped at 1000ft. Increase the airspeed and you'll have more lift to negate the higher mass. The increased airspeed also means your horizontal distance will be covered faster. The lead glider will travel the same path as the normal one but will be going a lot faster. The reason why gliders are built as light as possible is reduce the work required to lift them, the speed at which to release them, and the interia required to turn them. You also have the benefit of being able to land them at a lower airspeed without injury.