Not to be rude, but you need a dictionary as apathy is sitting down like the colonists at Pax in Serenity the Firefly movie. The Orks doesn't sit down and die, they rather rampage and kill, a whole different sort of action.
And just for a demonstration
http://www.urbandictionary.com/define.php?term=Apathy
Not to be rude but I think you should play attention in language classes a bit more.
Let's pretend we're an inquisitor whose in the know. They're fully aware that there's a swarm of countless aliens from outside the galaxy poised to strike anywhere at anytime. Not only that they're being drawn by the very thing that allows your ships to navigate the warp.
On any planet humans could start worshiping the dark gods and best case scenario they start a rebellion. Worst case they summon a daemon and things go down hill from there.
There's an entire race of raiders who could hit any planet at any time for the express purpose of taking humans to torture for their own amusement.
At any time their "good" cousins could choose to manipulate events so that people die or cause a war to start.
Under any planet millions of years old robots could arise or be awakened by the mechanicus and slaughter an entire planet.
On many planets orks could come and rampage slaughtering everything in their path.
Then there's the tau who are slowly subverting imperial plants into their own empire, every regiment and chapter sent to take that planet back is less resources to combat the other threats.
And finally to top it all off there's a negative space wedge filled with ten thousand year old super human warriors who launch a crusade every so often.
Any one of these is a threat, but they're all happening at the same time.
The other factions have their own problems. But the orks, well the only thing an ork cares about is how hard he can hit something with his choppa, or how fast he can charge at the enemy.
They don't care that there's countless threats ready to conquer the galaxy, their only concern is getting a good fight.
