humans
I am sure that the most proficient and expert over 20,000 hours experience pilots can recall at least one mistake that could have had very bad consecuences hadn't it been for a take off configuration alarm or a first officer, or similar, that warned them about their mistake.
Less experienced pilots maybe not, because it hasn't happened yet to them.
humans make mistakes. Even gifted ones. I've seen it happen.
Even Messi can shoot a penalty and send the ball to the 60th row.
The swiss cheese was there: maintenance, pressure, FO with low experience, bad company SOPs that didn't adopt manufacturer recommendations about an item in line with the maintenance cheese loaf and a mistake in line with the maintenance cheese loaf.
all together are to blame