Computers are built and programmed by humans.
Computers cannot think.
A computer will literally do exactly what it is told. If it has been misprogrammed to fly towards a cliff, or below MSA then it will do so.
Errors are made, databases have been wrong.
Some of these errors are not apparent during testing and validation. They only appear one day when an unforeseen unique set of circumstances arise.
NASA's Apollo 11 LEM computer was taking it towards a boulder field to land, until the human pilot, a certain Mr Armstrong, took manual control and vectored it clear.
In the event of failures of aircraft systems, the computer(s) may not have been programmed to respond appropriately, or may be incapable of responding correctly owing to loss of hydraulics or electrics or atmospheric measurement. That's why you always need humans in the loop.
Humans are not infallible of course. This is why you need two of them, and proper, thorough training, proper experience, and properly rested and motivated crews. Today's economics has taken precedent over this and we are seeing the results - a series of crashes and incidents that should never have happened.
I think it is significant that these 'automation dependant' crashes have started occuring now that pilots go from small training piston aircraft straight onto modern jets, missing out what used to happen - which was a few year's apprenticeship on turbo props, actually flying the aircraft and learning the ropes in a commercial environment, and applying all the things that had been learned in the ground school.