I'm going to guess as an island species, it had no natural predators, and therefore the evolutionary pressure for it to have a wide field of view did not exist
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
There was an interesting study done with zebra finches. In it they glued fake mohawkes on males and found that females selected them over unaltered males, even though it didn't naturally occur in the species. So there is some precedence for the possibility that the forward facing eyes were simply "sexier".
I mean, it it has pupils like that, it has a wide field of vision. That's the whole point of rectangular pupils. I would assume that having front-facing eyes would also give it depth perception, but maybe it needed that for making difficult jumps or something?