the system switches the elevator control from normal mode to a protection mode in which the AoA is proportional to the sidestick deflection. It simply did NOT happen here.
...for very obvious reasons which are very well documented in the report.
The crew had to recover from a stall situation by using the usual load factor demand law, something that Airbus itself had probably never tested before …
...or considered probable. It's all very nice to preach about need to install the Big Red Button that puts the beast into direct law. Issues here are a) whether it is realistic to expect the flightcrew to recognize exactly what's going on and react promptly b) whether misuse of manual override represents greater hazard than automation malfunction (e.g. some aeroplanes have no manual ground spoilers extensions to prevent their airborne deployment by mistake). Nevermind the control laws, the crew succesfuly recovered from the first stall. Second stall precipitated by full nose-up trim was fatal.
The technical options adopted by Airbus are unbelievably complex, and one cannot realize or foreseen the consequences of deteriorated data as sent to the system and how this all concept of flight control laws and protections will interact.
I don't find them unbelievably complex but that's just me. There's no need to predict the behaviour in details as long as the crew recognize it as undesirable and avoids the precursors to it - unless you're doing hard EGPWS or windshear escape there's no need to go anywhere near protections while flying the electric passenger jet. Freezing of the AoA propbes has happened before and test crew stopped the test when no autotrim cut-out was observed at calculated speed.
Why focus on the lastest (cockpit) ?
Because it's where the buck stops and buck's braking action here was severly poor.