Perhaps they simply don't need all that weight lifting capacity.
The A340 was simply an A330 with two extra engines and a longer fuselage. The A330 originally had exactly the same wing as the A340 (maybe still does), complete with hard points for the pylons for the A340's extra engines.
This proved very useful when it came to turning the A330 into an in flight refuelling tanker for air forces. There was already somewhere to bolt the in-flight refuelling hose reels (for the non-boom variant). That made the conversion incredibly cheap and low risk.