Earlier quoted context omitted.
"I take full responsibility" is always referred to the investors and shareholders. aka "I admit I have done a bad decision when I over hired and I'm correcting it". It's not a "I take full responsibility" towards the employees or customers.
Right, but the letters are typically directed towards employees.
They are taking the responsibility for having overhired and are acting on this responsibility by laying off.
They are not taking responsibility in front of laid off staff in any actionable way but "you can blame me rather than human resources, PMs that cried for more engineers, investors that were looking for signs of growth via head count..." which again is a sign of taking responsibility in front of shareholders, not really employees.