I think "back in the day", if eyes weren't available, eyes weren't installed. On the flip-side, I think in this day and age, it's just a way to offer a slightly different model of a plug you already have bodies for
..one more way to
corner the market
....it's just another reason to have more plugs tooo....
"yeah, I have some BM Dannys .... some with eyes, some without" -
I don't think they make much of a catching difference, unless you're counting fishermen of course ...
In saying that, If I'm looking to imitate a baitfish, obviously...I would prefer them to have eyes.