Middle East carriers also have geography on their side.
The UK - Oz market is about 3m single journeys p.a. (c0.9m Australians vising the UK & x0.6m the other way). A reasonable proportion will live outside the South East and they have a one stop service to SYD, MEL, BNE & PER, something not offered by othe carriers. (SQ's MAN flight now stops off at MUC.)
Flights to the Indian sub-continent will be as quick as travelling via LHR. (You can argue as to which of LHR, DXB, DOH or AUH offers the best transfer service.)
The last time I checked there were seven daily flights to the ME from Manchester (EK x 3 incl an A380, EY/'QR x 2) whilst EK has a further four flights from regional airports (BHX x 2, NCL & GLA).
EK also operates 3 x faily from LGE - very useful for those living south of London.
Services are also starting from DUB together with a number of European regional airports.
The UK APD for a family travelling to Oz id very high. It is relatively cheap to take the ferry to the Netherlands. I don't know about the cost of long term parking at Schiphol but could be a lot cheaper to fly out of AMS.
Then of course little or no tax is charged either on salaries or profits in the ME with public expenditure financed from oil & gas revenues. (Less true for the Emirate of Dubai rather than Abu Dhabi or Qatar.) This does give the ME carriers a cost advantage.
However as other posts have said, the Europe - ME /Asia market is finite and as new non stop routes are started the share of the ME carriers will stop rising. A few years ago SQ was growing exponentially, its growth is far more modest now. The rate of growth has to slow at some stage.