The Why of Laser Eyes
Between 80 and 90 percent of undersea life has some form of bioluminescence according to Edith Widder's TED Talk, "Glowing Life in an Underwater World" which means that as far as life on Earth is concerned, the emanation of radiation is predominant. The rule rather than the exception. Life finds the transmission and reception of waves as incredibly valuable, whether sound waves or light waves or other electromagnetic spectrum segments. Butterflies can position themselves globally for their annual migration simply using internal biological clocks and the position of the Sun over the horizon... that one point of EM data translated into a precise satellite-free GPS that fits in the pinhead of a butterfly's neural network.
Focused or targeted waves have even more utility. It's why sound waves became predominate on land and why bioluminescence took over undersea. It adds communication and more to the ability. It is, in fact, possible to create a biological laser. A laser increases transmission distances and intention.
Humanoid creatures have the evolutionary advantage of large scale flexible cooperative coordination. Insects have large scale coordination but are inflexible... they can act only in relatively narrow programmatic parameters. Higher order animals show far more flexibility, but fall apart if attempting large scale coordination... nothing on the order of insects. Humanoids, however, are able to entertain and maintain abstractions (like law, religion, community, etc) through communication and language.
Imagine a species which gains the ability to telecommunicate over line-of-sight through laser light. They would be able to coordinate over greater distances, faster, more complex ideas (than shouting, smoke signals, etc) and evolve greater and faster sophistication sooner with less conflict. Those able to communicate over longer distances, faster, with more intensity and accuracy are selected and the laser vision gets better and better.
The next step and adaptation for humanoids is learning to cook one's food. Instead of being entirely obsessed with the acquisition of one's daily calories, the advent of cooking frees more calories per eating instance, which accordingly frees time to ruminate, invent, innovate, and create a role of intelligence. The advanced communicators already had an evolutionary advantage of coordinating with other groups, warding off competition and predators, and corralling prey in exhausting marathon hunts where herds found themselves cut-off by lightspeed maneuvers until run ragged, captured and eaten by the fledgling Kryptonians.
At one time or another, a Kryptonian decides to flash his eyes at his food and finds that he's stronger for it. Evolution begins to select for more intense, hotter, more powerful eyes for cooking, above and over, what's necessary for communication. Such selection isn't undermined by technology (the advent of fire) because it's still an integral part of their hunting, feeding, community, culture. Soon Kryptonians are self-selecting for laser strength above and beyond what nature would do and it becomes selectively bred to an obscene degree.