The eyes of a scallop They are the dots you see when the shell opens

I mean it makes sense. Neurons are for coordination, so in order to coordinate more effectively, more information is an evolutionary advantage. The simplest eyes are just light sensors, neurons that evolved to breach the skin and detect the presence of light and transmit that information back to the ganglia. Super useful for early sea life that needed to know which way is up to orient themselves properly. And of course higher fidelity visual imagery, being able to distinguish between colors, etc all have their own advantages for survival, so these simple eye spots became increasingly complex.