Their ULH routes are extra costly. It's only natural to reduce capacity/frequency when yields and loads are low, or that extra capacity can go onto a better performing route.
The morning flight ex-SYD (EK415) still doesn't make sense to me. They tried it before it didn't go well (they said that the aircraft was put for better use elsewhere). Now they have it daily.
For weeks ahead it's wide open. Even during the peak period of end of June/mid July there is availability down to B buckets. And the busiest days are naturally on Saturdays. From a scheduling point of view it is a nicely timed flight for onward connections. But it's a horrid thing to go to SYD at 3 in the morning (unless you're a party animal and the idea of clubbing on two consecutive nights on both sides of the world fancies you).
Maybe that EK218 has similar issues for its odd timing from LAX despite connecting well with the PM flights from DXB.