AFAIK B copied MCAS from the Poseidon where it did use both AOAs. And it had a comparator warning if the 2 disagreed. To prevent the need for extra training on that warning for the MAX the decision was made to have MCAS use 1 AOA at a time, switching between left and right AOA with every power cycle. So it was connected to both AOAs, but would only use one per flight cycle.