> It doesn't seem like it should matter where you look when doing something unrelated to your eyeballs, such as making a salad, or riding a bike. After all, the eyes move independent of the rest of the body, right? So why is it relevant where we look when lifting a weight, if all the other parts of the body are moving properly?

Prompts to “look straight ahead” and such in a gym context are usually so you maintain the correct position of your neck and avoid injury.