Depth perception is advantageous. It is even beneficial for island goat activities.

With the absence of natural predators, the disadvantages of the narrow field of view are mostly outweighed by the advantages of depth perception .

Not necessarily, with “genetic drift” random phenotypic changes can happen that have a neutral effect on fitness. So if they don’t need side-facing eyes, then this can just happen randomly. Especially if the sideways eyes are in some way “costly” to maintain

I'm not sure for that specific case, but in the general case there doesn't need to be evolutionary pressure for change. If there is no pressure one way or the other random mutations can (and will over time) cause change without environmental reason (genetic drift).

maybe living in caves?