It's probably just a matter of trade-offs. The visible range does cover the peak energy of the spectrum of sunlight, and covering more of the infrared may just

It's probably just a matter of trade-offs. The visible range does cover the peak energy of the spectrum of sunlight, and covering more of the infrared may just not be worth the cost of a more complicated eye. It would be interesting to see some type of measure of the information content of adding more infrared in typical nature scenes.