I don't think I've ever heard of anyone using the black glove mount rings. Those are for gloves with an attached lining correct, thicker than just the thin cotton or poly liner flocking in like a 660 or 720? I'm sure nearly everyone that needs fatter gloves with thick liners is using something like a showa 495 with their own liners rather an insulated glove like a 490 with a liner that can't be removed. If my understanding is correct, almost no one would need the black rings, so not supplying them is a really good idea if it helps them control costs.
The rolock 90 set I picked up recently from drysuitspareparts came with the black rings, so I have an extra set of black glove mount rings I have no real use for either. I suspect they are still previous stock rolock 90 kits, which is why they still contain the black rings and they why still sell for the 2023 price.