This is a good question.
A number of possible answers (and no, pilot skill not the only one - though everyone is focusing on that and boeing).
Maintenance.
This issue develops IF the computer gets bad data from a sensor.
Question - would this sort of thing get fixed more quickly in the US?
For the Ethiopian crash we have in days leading up to crash errors in the system - all different flights
* Capt side altimeter erratic, showed a decent and lower level then back to normal.
* During approach at 1000' the aircraft started to roll right with the auto pilot engaged.
* During approach at 8K altimeter rapidly descended and returned to normal - caused autopilot problems.
* During takeoff altitude and vert speed on both PFDs showed erratic indications
For Lion Air in days leading up an increase in warnings. Some excerpts.
* Speed trim fail light and mach trim fail light
* Auto throttle diconnect
* Speed and Alt flag
* Feel diff pressure - fail light illuminated
* Maintenance light illuminated during landing
Regulatory regime
What's the local situation in terms of check rides, maintenance monitoring and cross checks, airline procedure monitoring etc. Ethiopia has a relatively stronger reputation here.
Training
The memory item in this situation is basically a revert to manual flight. There is a possibility that manual flight is not as common in some countries, particularly if they don't have a large General Aviation pool to pull from. This is a concern in US as well (automation reliance).
The path to getting onto a jet in US is currently different than other places. To be a first officer takes 1,500+ hours and an ATP. That's a pretty high bar.
This is a design issue I think as well -> should Boeing reasonably consider that there may be differences between pilot groups in terms of training pathways. I would suggest obviously yes. Is the FAA at fault because other countries may choose different approaches? That's less clear to me. BTW the FAA did a terrible job for a while with small charter operators in financial distress with bad maintenance for example - so the FAA has blindspots but their Part 121 stuff has a good record so far.
The US system has had some amazing saves -> failures with airport bird control -> capt sully etc. Often these pilots aren't jet fighter pilots but have things like glider or small plane experience that is helpful. So systems break down in US, but saves happen.
My US worries are maintenance given cost pressures and actually Air Traffic Control (given fatigue and some weakening of standards there around new hiring).