The difference is that all Airbus planes since the 1980's A320 are built around computerized flight commands, so the code paths involved are exercised constantl

The difference is that all Airbus planes since the 1980's A320 are built around computerized flight commands, so the code paths involved are exercised constantly. MCAS only triggers occasionally, meaning if it has a bug, it only shows up at the worst possible time. Airbus planes also have double redundancy (three inputs and computers) for all those systems, where MCAS had none by default.