No clue why the YC doesn't do this as well, other than different management philosophy. All I know is that in 2015 we had a 3 resort split stay and multiple bands. All bands worked just fine at AK and Poly, but only 1 was allowed at BC. I ran into the General Manager of BC while there and asked about it. I was told every resort has that same option, but BC is the only one that routinely implements the option and it's only so they don't have to deal with the SAB issue. Front desk CMs are generally unaware of how the technology works, let alone how the resort has chosen to configure the technology. CMs still fall back on the misconception that MB problems are a result of guests having too many (i.e. more than 1) Magic Bands on their account. It's always easier to just blame the technology and reset the connection to a band.
Keycards are merely another version of a Magic Band. Same tech, different form factor.
Steve