The optional 18" wheels for BB are the same as to what are the standard wheels for OB. So I could see there being a shortage of those wheels and them remvoing the option for BB in order to fullfill the OB orders.I do know that the optional 18" Wheel for Big Bend are no longer available. It was disclosed on the last Dealer Order Guide (05/01/21) that was posted to this forum. Maybe they are thinking OB instead of BB?
18” Machined-face Aluminum Ebony Black-painted Wheel “Not Available for the remainder of the 21MY” 6
For details as to what is no longer available - go here.