Both computers have access to both sensor's data. The computers are networked together. This is how they implement the AoA disagree function (the one which was

Both computers have access to both sensor's data. The computers are networked together. This is how they implement the AoA disagree function (the one which was broken in 90% of MAXes for unrelated reasons). It's also how they managed to implement a software update which makes MCAS take data from both sensors. The logic for not implementing both sensors is much more insidious. If you implement both sensors, then you have to deal with the case that infomation from sensors might disagree. The computer has no idea sensor is providing correct data, so the only thing it can really do is disable itself when the sensors disagree. If MCAS has the ability to disable itself, then it must provide feedback to pilots it has done so, and have pilots follow some procedures. If there were procedures, then Boeing would have to add pilot training about what MCAS was and how things would be different when it disabled itself. Boeing made it rely on only a single sensor to bypass training requirements.