Giant mecha are already implausible.

Not only is the humanoid form impractical and inefficient for a machine per se, it's also immensely impractical for a machine which is 10 times the height of a human. Human legs wouldn't be an efficient way of locomotion due to the square-cube law. There is too little gravity and most surfaces would be far too soft for a robot of that size to walk like a human would. It would be like walking in a swamp on the moon.

There is really just one reason to build giant mecha: Aesthetics. You are building a humanoid mech because you want it to look humanoid. Which means that your priority is already aesthetics over practicality. Which also means you are going to give your creation a human-looking face, even when most of its facial features aren't even functional.

So those things on its face aren't actually its optical sensors. They are just for show. The actual optical sensors are much smaller and hidden elsewhere.

Giant mecha are already implausible.

Not only is the humanoid form impractical and inefficient for a machine per se, it's also immensely impractical for a machine which is 10 times the height of a human. Human legs wouldn't be an efficient way of locomotion due to the square-cube law. There is too little gravity and most surfaces would be far too soft for a robot of that size to walk like a human would. It would be like walking in a swamp on the moon.

There is really just one reason to build giant mecha: Aesthetics. You are building a humanoid mech because you want it to look humanoid. Which means that your priority is already aesthetics over practicality. Which also means you are going to give your creation a human-looking face, even when most of its facial features aren't even functional.

So those things on its face which look like eyes aren't actually its optical sensors. They are just for show. The actual optical sensors are much smaller and hidden elsewhere.