… people who are really crap at their job remain employed (or, were ever employed in the first place)?
It just annoys me that things are expected of me and colleagues when they, themselves, are, to put it mildly, almost incompetent.
Grrr.
by 
How come……
by
“They”?
People who are really crap at their job remain employed because the purpose of society is not efficiency. Human beings themselves are notoriously inefficient parasites. This includes you and me.
More on this at Efficiency vs Well-being.
Cheers.
OK, well, ‘he’ but as you point out, there are many of these ‘he’s’ (and, for that matter, ‘she’s’) so that ‘they’ as a general term is still applicable. It was a bad day, you understand