Interesting! I love trying to figure out how the environmental factors + anims' physiology create what I'm seeing.
It could also be that in a small island where food is closer, seeing distant isn't worth the cost, since good eyesight uses more energy/nutrients every metabolic cycle. (Eyesight in Vilmonic increases the amount of objects processed by their graph-brains every metabolic cycle.)
You could set up an experiment to test this! Maybe something like this:
A very horizontal island with fungs on one half, a "wasteland" of stone floor in the middle, and water on the right. This setup seems like it would tend to evolve anims with greater eyesight, so that they could navigate the long distance from food to water.
Strategic placement of floors and walls can have a surprising effect on evolving certain traits! For instance, sparse placement of obstacles/walls can make it just a bit harder for anims to over-graze, helping fungs to flourish.