They are not. You are doing it wrong. 

The day we moved into our present apartment, we were fresh off the plane, didn't have anything but a couple of suitcases, a dog and some small stuff. A friend of my wifes family brought us some duvets, my mother in law some duvet covers, and they also brought some help. In all 4 women, 50+ age group helped us move in, despite having nothing to move. 

They cleaned out bedroom (the entire apartment had already been Ayi'ed for an entire day prior) and made the bed. 4 women, after 15+ minutes had not managed to get the duvet cover under control for a 200x220cm duvet. I was hungry, and as a sign of good faith and appreciation of their efforts I showed them how.

Step one: Place the duvet flat, so head/foot end is correct. 

Step two: Figure out if the opening in the duvet cover is at the side or the foot end

Step three: Flip the duvet cover inside out.

Step four: Put you arms inside the duvet cover, a hand at either corner at the end/side away from the opening, so you are grabbing the corner from the inside

Step Five: Through the cover, grab the duvet, do a quick yank and you're done...... or so it would be had it not been for the small openings. 

Extra Step 6 for China duvet covers. Still keeping a grip on the corners from the inside, grab both with one hand, use the other hand to help the cover around the duvet.

Step 7 (or 6 depending if you did the other step 6) Shake everything about a bit, zip and goodnight. 

I find the pillow cases impossible.  It seems the zippers always break.