Route offset in China
 

If you flew to China often, you will notice that the ATC constantly gives you route offset, and the number is usually different when switching to different zones (3nm, 5nm, 6nm etc.). Is there a main reason for this and why does is not happen in other countries often?

China has very few airways, most cities are connected by just one possible route.
To permit level changes on an airway with traffic going either way everyone is taken right of route (normally) to gain the required separation.

Were it only so, I was one level above a QR Airbus a year ago entering China from Yangon Control. He'd been looking for higher and I was unable to climb any higher. Kunming (?) gave me 5nm right offset. Great, I thought, QR will the climb he was looking for, both bound for Shanghai. Just then, Control tells QR, "offset Romeo of course 5 nm." I kid you not.