Excellent response from
@EnolaGaia . Thank you.
Evolution is a mathematical process, not an intelligent one. On the basis of probabilities, evolution "selects in" things that aid reproduction, and it "selects out" things that hamper reproduction.
In a lightless cave, eyes no longer aid a creature in reaching sexual maturity, breeding, and successfully raising its young. There is no probability pressure in favour of eyes.
Eyes are complex, and require a substantial energy budget to grow and maintain. They are also vulnerable to injury or infection. In a closed cave system, where the energy supply is limited, wasting energy on growing and maintaining eyes reduces a creature's chance of reaching sexual maturity, breeding, and successfully raising its young. The probability pressure is therefore in the direction of no eyes.
In a small closed population, the rate of change will be greater because a small number of mutant genes is less diluted.