The others have answered from a physics standpoint, but this also has an evolutionary reason: Our eyesight is probably centered upon green because of the prevalent form of photosynthesis on our planet. There are many forms of light conversion that could have evolved, in fact it's believed that before blue-green cyanobacteria (plants) there were purple bacteria that converted the sunlight.
Humans are omnivores, so that not only can differentiating between shades of green plant help us find plants to eat and avoid poisonous ones, but it can help us find prey animals that are seeking specific kinds of plants.
Remember that the three colors we see are not objectively special colors. They are simply one color for each of the three kinds of cones our eyes have. We could have evolved cones that detect ultraviolet, orange, and infrared, or any other set of colors, or even another number of different colors. We could have had five cones sensing any five colors, or two. Some other animals have only one (therefore see only one color), birds have four, mantis shrimp have 12.
Had purple bacteria become the photoplasts in the cells of land plants, instead of green bacteria, our eyesight may be centered on purple, instead of green, if random chance and our genes had combined to allow that.
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