As usual with biologists, if they do not understand what it does they claim it's a useless byproduct of evolution. A few years later they discover there is actual purpose to it, and it is actually pretty nifty. Rinse and repeat.

Wonder what would happen if an octopus looked directly at the sun

I have heard the theory that it evolved this way for higher UV protection that was not needed in underwater organisms. Curious if it was really that much of a competitive advantage though.

Edit: okay more recent studies show not so much protection but basically filtering and redirecting light so out eyes can see better color on land. See this comment: https://lemmy.world/comment/18892927