Well, there's the problem. Boeing and the FAA thought pilots could pilot planes without AOA indicators or AoA disagree alerts. They have been optional on the 737 line for decades and the planes flew very well.
But prior to the 737 MAX AoA sensor data was not a control input. It was an information input to the pilots and warning systems. No control system acted on input received from the AoA sensors. If installed AoA sensors malfunctioned, the worst the plane's systems would do is start throwing alerts to the pilots or, if they had the optional AoA indicators, show weird numbers on those indicators.
With the 737 MAX, AoA sensors are not optional, they are critical flight control input. That is, control systems now directly act on data received from the AoA sensors, unlike with the previous 737 versions, and MCAS adjusts the TRIM automatically and directly from AoA sensor input. Therefore having the "AoA disagreement light" remain an optional feature, even though AoA data is now critical flight-input and automatic control adjustment data, is negligent at best.
The core of the problem is that Boeing intentionally downplayed, if not hid, MCAS and how it worked and how to respond to it, intentionally failed to require pilots to train on this system, to protect sales.